Updated on 2022/12/02

写真a

 
MAEDA, Keiichi
 
Scopus Paper Info  
Paper Count: 0  Citation Count: 0  h-index: 19

Citation count denotes the number of citations in papers published for a particular year.

Affiliation
Faculty of Science and Engineering
Job title
Professor Emeritus

Degree

  • 京都大学   理学博士(京都大学)

Professional Memberships

  •  
     
     

    国際天文連合

  •  
     
     

    一般相対性および重力学会

  •  
     
     

    日本天文学会

  •  
     
     

    日本物理学会

 

Research Areas

  • Theoretical studies related to particle-, nuclear-, cosmic ray and astro-physics

Research Interests

  • Cosmology, Relativity, Astrophysics, Particles Physics

Papers

  • A possible solution to the helium anomaly of EMPRESS VIII by cuscuton gravity theory

    Kazunori Kohri, Kei-ichi Maeda

    Progress of Theoretical and Experimental Physics   2022 ( 9 )  2022.09  [Refereed]

     View Summary

    Abstract

    We discuss cosmology based on the cuscuton gravity theory to resolve the anomaly of the observational 4He abundance reported by the EMPRESS collaboration. We find that the gravitational constant Gcos in the Friedmann equation should be smaller than Newton’s constant GN such that ${\Delta G_{\rm N } }/{G_{\rm N } } \equiv (G_{\rm cos}-G_{\rm N})/{G_{\rm N } } = -0.085_{-0.028}^{+0.026} \ (68 \% \text{ C.L.})$ in terms of big-bang nucleosynthesis, which excludes ΔGN = 0 at more than 95% C.L. To fit the data, we obtain a negative mass squared of a non-dynamical scalar field with the Planck-mass scale as $\sim - {\mathcal {O } }(1) {M_{\rm PL}^2} ({\mu }/{0.5 M_{\rm PL } })^{4}$ with the cuscuton mass parameter μ. This fact could suggest the need for modified gravity theories such as the cuscuton gravity theory with a quadratic potential, which can be regarded as the low-energy Hořava–Lifshitz gravity, and might give a hint of quantum gravity.

    DOI

  • Comparison of two theories of Type-IIa minimally modified gravity

    Antonio De Felice, Kei-ichi Maeda, Shinji Mukohyama, Masroor C. Pookkillath

    Physical Review D   106 ( 2 )  2022.07  [Refereed]

    DOI

  • Cuscuta-Galileon cosmology: Dynamics, gravitational constants, and the Hubble constant

    Kei-ichi Maeda, Sirachak Panpanich

    Physical Review D   105 ( 10 )  2022.05  [Refereed]

    DOI

  • ECO-spotting: looking for extremely compact objects with bosonic fields

    Vitor Cardoso, Caio F B Macedo, Kei-ichi Maeda, Hirotada Okawa

    Classical and Quantum Gravity   39 ( 3 ) 034001 - 034001  2022.02  [Refereed]

     View Summary

    Abstract

    Black holes are thought to describe the geometry of massive, dark compact objects in the Universe. To further support and quantify this long-held belief requires knowledge of possible, if exotic alternatives. Here, we wish to understand how compact can self-gravitating solutions be. We discuss theories with a well-posed initial value problem, consisting in either a single self-interacting scalar, vector or both. We focus on spherically symmetric solutions, investigating the influence of self-interacting potentials into the compactness of the solutions, in particular those that allow for flat-spacetime solutions. We are able to connect such stars to hairy black hole solutions, which emerge as a zero-mass black hole. We show that such stars can have light rings, but their compactness is never parametrically close to that of black holes. The challenge of finding black hole mimickers to investigate full numerical-relativity binary setups remains open.

    DOI

  • Post-Newtonian Kozai-Lidov mechanism and its effect on cumulative shift of periastron time of binary pulsar

    Haruka Suzuki, Priti Gupta, Hirotada Okawa, Kei Ichi Maeda

    Monthly Notices of the Royal Astronomical Society   500 ( 2 ) 1645 - 1665  2021.01  [Refereed]

     View Summary

    We study the Kozai-Lidov mechanism in a hierarchical triple system in detail by the direct integration of the first-order post-Newtonian equations of motion. We analyse a variety of models with a pulsar to evaluate the cumulative shift of the periastron time of a binary pulsar caused by the gravitational wave emission in a hierarchical triple system with Kozai-Lidov mechanism. We compare our results with those by the double-averaging method. The deviation in the eccentricity, even if small, is important in the evaluation of the emission of the gravitational waves. We also calculate the cumulative shift of the periastron time by using obtained osculating orbital elements. If Kozai-Lidov oscillations occur, the cumulative shift curve will bend differently from that of the isolated binary. If such a bending is detected through the radio observation, it will be the first indirect observation of gravitational waves from a triple system.

    DOI

  • Kink-antikink collision in a Lorentz-violating ϕ4 model

    Haobo Yan, Yuan Zhong, Yu-Xiao Liu, Kei-ichi Maeda

    Physics Letters B   807   135542 - 135542  2020.08  [Refereed]

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    16
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  • Gravitational waves from hierarchical triple systems with Kozai-Lidov oscillation

    Priti Gupta, Haruka Suzuki, Hirotada Okawa, Kei Ichi Maeda

    Physical Review D   101 ( 10 )  2020.05  [Refereed]

     View Summary

    We study gravitational waves from a hierarchical three-body system up to first-order post-Newtonian approximation. Under certain conditions, the existence of a nearby third body can cause periodic exchange between eccentricity of an inner binary and relative inclination, known as Kozai-Lidov oscillations. We analyze features of the waveform from the inner binary system undergoing such oscillations. We find that variation caused due to the tertiary companion can be observed in the gravitational waveforms and energy spectra, which should be compared with those from isolated binaries and coplanar three-body system. The detections from future space-based interferometers will make possible the investigation of gravitational wave spectrum in mHz range and may fetch signals by sources addressed.

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    18
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  • Stability of hybrid Higgs inflation

    Seiga Sato, Kei-ichi Maeda

    Physical Review D   101 ( 10 )  2020.05  [Refereed]

    DOI

  • Maximal efficiency of the collisional Penrose process with a spinning particle. II. Collision with a particle on the innermost stable circular orbit

    Kazumasa Okabayashi, Kei-ichi Maeda

    Progress of Theoretical and Experimental Physics   2020 ( 1 )  2020.01  [Refereed]

     View Summary

    Abstract

    We analyze the collisional Penrose process between a particle on the innermost stable circular orbit (ISCO) orbit around an extreme Kerr black hole and a particle impinging from infinity. We consider both cases with non-spinning and spinning particles. We evaluate the maximal efficiency, $\eta_{\text{max } }=(\text{extracted energy})/(\text{input energy})$, for the elastic collision of two massive particles and for the photoemission process, in which the ISCO particle will escape to infinity after a collision with a massless impinging particle. For non-spinning particles, the maximum efficiency is $\eta_{\text{max } } \approx 2.562$ for the elastic collision and $\eta_{\text{max } } \approx 7$ for the photoemission process. For spinning particles we obtain the maximal efficiency $\eta_{\text{max } } \approx 8.442$ for the elastic collision and $\eta_{\text{max } } \approx 12.54$ for the photoemission process.

    DOI

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    9
    Citation
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  • Cosmological dynamics and double screening of DBI-Galileon gravity

    Sirachak Panpanich, Supakchai Ponglertsakul, Kei-ichi Maeda

    Physical Review D   100 ( 4 ) 044038  2019.08  [Refereed]

  • Cumulative shift of periastron time of binary pulsar with Kozai–Lidov oscillation

    Haruka Suzuki, Priti Gupta, Hirotada Okawa, Kei Ichi Maeda

    Monthly Notices of the Royal Astronomical Society: Letters   486 ( 1 ) L52 - L57  2019.06  [Refereed]

     View Summary

    We study a hierarchical triple system with the Kozai–Lidov mechanism, and analyse the cumulative shift of periastron time of a binary pulsar by the emission of gravitational waves. Time evolution of the osculating orbital elements of the triple system is calculated by directly integrating the first-order post-Newtonian equations of motion. The Kozai–Lidov mechanism will bend the evolution curve of the cumulative shift when the eccentricity becomes large. We also investigate the parameter range of mass and semimajor axis of the third companion with which the bending of the cumulative-shift curve could occur within 100 yr.

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    5
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  • Metric-affine gravity and inflation

    Keigo Shimada, Katsuki Aoki, Kei-ichi Maeda

    Physical Review D   99 ( 10 )  2019.05  [Refereed]

    DOI

  • α-attractor-type double inflation

    Kei-ichi Maeda, Shuntaro Mizuno, Ryota Tozuka

    Physical Review D   98 ( 12 )  2018.12  [Refereed]

    DOI

  • Maximal efficiency of the collisional Penrose process with spinning particles

    Kei-Ichi Maeda, Kazumasa Okabayashi, Hirotada Okawa

    Physical Review   D.98 ( 064027 )  2018.09  [Refereed]

     View Summary

    © 2018 American Physical Society. We analyze the collisional Penrose process of spinning test particles in an extreme Kerr black hole. We consider that two particles plunge into the black hole from infinity and collide near the black hole. For the collision of two massive particles, if the spins of particles are s1≈0.01379 μM and s2≈-0.2709 μM, we obtain the maximal efficiency is about ηmax=(extracted energy)/(input energy)≈15.01, which is more than twice as large as the case of the collision of non-spinning particles (ηmax≈6.32). We also evaluate the collision of a massless particle without spin and a massive particle with spin (Compton scattering), in which we find the maximal efficiency is ηmax≈26.85 when s2≈-0.2709 μM, which should be compared with ηmax≈13.93 for the nonspinning case.

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    14
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  • Hybrid Higgs inflation: The use of disformal transformation

    Seiga Sato, Kei-Ichi Maeda

    Physical Review D   97 ( 8 ) 13pp  2018.04

     View Summary

    We propose a hybrid type of the conventional Higgs inflation and new Higgs inflation models. We perform a disformal transformation into the Einstein frame and analyze the background dynamics and the cosmological perturbations in the truncated model, in which we ignore the higher-derivative terms of the Higgs field. From the observed power spectrum of the density perturbations, we obtain the constraint on the nonminimal coupling constant ξ and the mass parameter M in the derivative coupling. Although the primordial tilt ns in the hybrid model barely changes, the tensor-to-scalar ratio r moves from the value in the new Higgs inflationary model to that in the conventional Higgs inflationary model as |ξ| increases. We confirm our results by numerical analysis by ADM formalism of the full theory in the Jordan frame.

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    12
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  • Massive graviton geons

    Katsuki Aoki, Kei-Ichi Maeda, Yosuke Misonoh, Hirotada Okawa

    Physical Review D   97 ( 4 )  2018.02  [Refereed]

     View Summary

    We find vacuum solutions such that massive gravitons are confined in a local spacetime region by their gravitational energy in asymptotically flat spacetimes in the context of the bigravity theory. We call such self-gravitating objects massive graviton geons. The basic equations can be reduced to the Schrödinger-Poisson equations with the tensor "wave function" in the Newtonian limit. We obtain a nonspherically symmetric solution with j=2, =0 as well as a spherically symmetric solution with j=0, =2 in this system where j is the total angular momentum quantum number and is the orbital angular momentum quantum number, respectively. The energy eigenvalue of the Schrödinger equation in the nonspherical solution is smaller than that in the spherical solution. We then study the perturbative stability of the spherical solution and find that there is an unstable mode in the quadrupole mode perturbations which may be interpreted as the transition mode to the nonspherical solution. The results suggest that the nonspherically symmetric solution is the ground state of the massive graviton geon. The massive graviton geons may decay in time due to emissions of gravitational waves but this timescale can be quite long when the massive gravitons are nonrelativistic and then the geons can be long-lived. We also argue possible prospects of the massive graviton geons: applications to the ultralight dark matter scenario, nonlinear (in)stability of the Minkowski spacetime, and a quantum transition of the spacetime.

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    6
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  • Condensate of massive graviton and dark matter

    Katsuki Aoki, Kei-Ichi Maeda

    Physical Review D   97 ( 4 ) 24pp  2018.02

     View Summary

    We study coherently oscillating massive gravitons in the ghost-free bigravity theory. This coherent field can be interpreted as a condensate of the massive gravitons. We first define the effective energy-momentum tensor of the coherent massive gravitons in a curved spacetime. We then study the background dynamics of the Universe and the cosmic structure formation including the effects of the coherent massive gravitons. We find that the condensate of the massive graviton behaves as a dark matter component of the Universe. From the geometrical point of view the condensate is regarded as a spacetime anisotropy. Hence, in our scenario, dark matter is originated from the tiny deformation of the spacetime. We also discuss a production of the spacetime anisotropy and find that the extragalactic magnetic field of a primordial origin can yield a sufficient amount for dark matter.

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    14
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  • Non-linear collisional Penrose process: How much energy can a black hole release?

    Ken-Ichi Nakao, Hirotada Okawa, Kei-Ichi Maeda

    Progress of Theoretical and Experimental Physics   2018 ( 1 ) 21pp  2018.01  [Refereed]

     View Summary

    Energy extraction from a rotating or charged black hole is one of the fascinating issues in general relativity. The collisional Penrose process is one such extraction mechanism and has been reconsidered intensively since Bañados, Silk, and West pointed out the physical importance of very high energy collisions around a maximally rotating black hole. In order to get results analytically, the test particle approximation has been adopted so far. Successive works based on this approximation scheme have not yet revealed the upper bound on the efficiency of the energy extraction because of the lack of backreaction. In the Reissner-Nordström spacetime, by fully taking into account the self-gravity of the shells, we find that there is an upper bound on the extracted energy that is consistent with the area law of a black hole. We also show one particular scenario in which almost the maximum energy extraction is achieved even without the Bañados-Silk-West collision.

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    6
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  • Cosmological and astrophysical Vainshtein mechanism in bigravity

    Katsuki Aoki, Kei-ichi Maeda, Makoto Tanabe, Ryo Namba

    Proceedings of the MG14 Meeting on General Relativity    2017.12

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  • Cosmological dynamics of D-BIonic and DBI scalar field and coincidence problem of dark energy

    Sirachak Panpanich, Kei-ichi Maeda, Shuntaro Mizuno

    PHYSICAL REVIEW D   95 ( 10 ) 15pp  2017.05  [Refereed]

     View Summary

    We study the cosmological dynamics of a D-BIonic and Dirac-Born-Infeld scalar field, which is coupled to matter fluid. For the exponential potential and the exponential couplings, we find a new analytic scaling solution yielding the accelerated expansion of the Universe. Since it is shown to be an attractor for some range of the coupling parameters, the density parameter of matter fluid can be the observed value, as in the coupled quintessence with a canonical scalar field. Contrary to the usual coupled quintessence, where the value of the matter coupling giving the observed density parameter is too large to satisfy the observational constraint from the cosmic microwave background, we show that the D-BIonic theory can give a similar solution with a much smaller value of matter coupling. As a result, together with the fact that the D-BIonic theory has a screening mechanism, the D-BIonic theory can solve the so-called coincidence problem as well as the dark energy problem.

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    5
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  • 非線形衝突ペンローズ過程によるエネルギー引き抜き効率について

    中尾 憲一, 大川 博督, 前田 恵一

    一般社団法人 日本物理学会 日本物理学会講演概要集   72 ( 0 ) 339 - 339  2017  [Refereed]

    DOI CiNii

  • AdS monopole black hole and phase transition

    Shoichiro Miyashita, Kei-ichi Maeda

    PHYSICAL REVIEW D   94 ( 12 ) 17pp  2016.12  [Refereed]

     View Summary

    We study the Einstein-SO(3) Yang-Mills-Higgs system with a negative cosmological constant and find the monopole black hole solutions as well as the trivial Reissner-Nordstrm black hole. We discuss thermodynamical stability of the monopole black hole in an isolated system. We expect a phase transition between those two black holes when the mass of a black hole increases or decreases. The type of phase transition depends on the cosmological constant Lambda, as well as the vacuum expectation value upsilon and the coupling constant lambda of the Higgs field. Keeping lambda small, we find there are two critical values of the cosmological constant, Lambda(cr(1)) (upsilon) and Lambda(cr(2)) (upsilon), which depend on upsilon. If Lambda(cr(1)) (upsilon) < Lambda(< 0), we find the first order transition, whereas if Lambda(cr(2)) (upsilon) < Lambda < Lambda(cr(1)) (upsilon), the transition becomes second order. For the case of Lambda(b) (upsilon) < Lambda < Lambda((2)) (upsilon), we again find the first order irreversible transition from the monopole black hole to the extreme Reissner-Nordstrm black hole. Beyond Lambda(b) (upsilon), no monopole black hole exists. We also discuss thermodynamical properties of the monopole black hole in a thermal bath system.

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    1
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  • Gravitational baryogenesis after anisotropic inflation

    Mitsuhiro Fukushima, Shuntaro Mizuno, Kei-ichi Maeda

    PHYSICAL REVIEW D   93 ( 10 )  2016.05  [Refereed]

     View Summary

    The gravitational baryogensis may not generate a sufficient baryon asymmetry in the standard thermal history of the Universe when we take into account the gravitino problem. Hence, it has been suggested that anisotropy of the Universe can enhance the generation of the baryon asymmetry through the increase of the time change of the Ricci scalar curvature. We study the gravitational baryogenesis in the presence of anisotropy, which is produced at the end of an anisotropic inflation. Although we confirm that the generated baryon asymmetry is enhanced compared with the original isotropic cosmological model, taking into account the constraint on the anisotropy by the recent CMB observations, we find that it is still difficult to obtain the observed baryon asymmetry only through the gravitational baryogenesis without suffering from the gravitino problem.

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    16
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  • Gravitational baryogenesis after anisotropic inflation

    Fukushima, Mitsuhiro, Mizuno, Shuntaro, Maeda, Kei Ichi

    Physical Review   D 93 ( 10 )  2016.05

     View Summary

    © 2016 American Physical Society.The gravitational baryogensis may not generate a sufficient baryon asymmetry in the standard thermal history of the Universe when we take into account the gravitino problem. Hence, it has been suggested that anisotropy of the Universe can enhance the generation of the baryon asymmetry through the increase of the time change of the Ricci scalar curvature. We study the gravitational baryogenesis in the presence of anisotropy, which is produced at the end of an anisotropic inflation. Although we confirm that the generated baryon asymmetry is enhanced compared with the original isotropic cosmological model, taking into account the constraint on the anisotropy by the recent CMB observations, we find that it is still difficult to obtain the observed baryon asymmetry only through the gravitational baryogenesis without suffering from the gravitino problem.

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    16
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  • Relativistic stars in bigravity theory

    Katsuki Aoki, Kei-ichi Maeda, Makoto Tanabe

    PHYSICAL REVIEW D   93 ( 6 )  2016.03  [Refereed]

     View Summary

    Assuming static and spherically symmetric spacetimes in the ghost-free bigravity theory, we find a relativistic star solution, which is very close to that in general relativity. The coupling constants are classified into two classes: Class [I] and Class [II]. Although the Vainshtein screening mechanism is found in the weak gravitational field for both classes, we find that there is no regular solution beyond the critical value of the compactness in Class [I]. This implies that the maximum mass of a neutron star in Class [I] becomes much smaller than that in general relativity (GR). On the other hand, for the solution in Class [II], the Vainshtein screening mechanism works well even in a relativistic star and the result in GR is recovered.

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    8
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  • Relativistic stars in bigravity theory

    Aoki, Katsuki, Maeda, Kei Ichi, Tanabe, Makoto

    Physical Review D - Particles, Fields, Gravitation and Cosmology   93 ( 6 )  2016.03

     View Summary

    © 2016 American Physical Society.Assuming static and spherically symmetric spacetimes in the ghost-free bigravity theory, we find a relativistic star solution, which is very close to that in general relativity. The coupling constants are classified into two classes: Class [I] and Class [II]. Although the Vainshtein screening mechanism is found in the weak gravitational field for both classes, we find that there is no regular solution beyond the critical value of the compactness in Class [I]. This implies that the maximum mass of a neutron star in Class [I] becomes much smaller than that in general relativity (GR). On the other hand, for the solution in Class [II], the Vainshtein screening mechanism works well even in a relativistic star and the result in GR is recovered.

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    8
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  • Black holes and Thunderbolt singularities with Lifshitz scaling terms

    Yosuke Misonoh, Kei-Ichi Maeda

    Physical Review D - Particles, Fields, Gravitation and Cosmology   92 ( 8 )  2015.10

     View Summary

    We study a static, spherically symmetric and asymptotic flat spacetime, assuming the hypersurface orthogonal Einstein-aether theory with an ultraviolet modification motivated by the Hořava-Lifshitz theory, which is composed of the z=2 Lifshitz scaling terms such as scalar combinations of a three-Ricci curvature and the acceleration of the aether field. For the case with the quartic term of the acceleration of the aether field, we obtain a two-parameter family of black hole solutions, which possess a regular universal horizon. Whereas, if a three-Ricci curvature squared term is joined in ultraviolet modification, we find a solution with a thunderbolt singularity such that the universal horizon turns out to be a spacelike singularity.

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    10
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  • Black holes and Thunderbolt singularities with Lifshitz scaling terms

    Yosuke Misonoh, Kei-ichi Maeda

    PHYSICAL REVIEW D   92 ( 8 )  2015.10  [Refereed]

     View Summary

    We study a static, spherically symmetric and asymptotic flat spacetime, assuming the hypersurface orthogonal Einstein-aether theory with an ultraviolet modification motivated by the Horava-Lifshitz theory, which is composed of the z = 2 Lifshitz scaling terms such as scalar combinations of a three-Ricci curvature and the acceleration of the aether field. For the case with the quartic term of the acceleration of the aether field, we obtain a two-parameter family of black hole solutions, which possess a regular universal horizon. Whereas, if a three-Ricci curvature squared term is joined in ultraviolet modification, we find a solution with a thunderbolt singularity such that the universal horizon turns out to be a spacelike singularity.

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    10
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  • Stability of the early universe in bigravity theory

    Katsuki Aoki, Kei-Ichi Maeda, Ryo Namba

    Physical Review D - Particles, Fields, Gravitation and Cosmology   92 ( 4 )  2015.08

     View Summary

    We study the stability of a spherically symmetric perturbation around the flat Friedmann-Lemaître-Robertson-Walker spacetime in the ghost-free bigravity theory, retaining nonlinearities of the helicity-0 mode of the massive graviton. It has been known that, when the graviton mass is smaller than the Hubble parameter, homogeneous and isotropic spacetimes suffer from the Higuchi-type ghost or the gradient instability against the linear perturbation in the bigravity. Hence, the bigravity theory has no healthy massless limit for cosmological solutions at linear level. In this paper we show that the instabilities can be resolved by taking into account nonlinear effects of the scalar graviton mode for an appropriate parameter space of coupling constants. The growth history in the bigravity can be restored to the result in general relativity in the early stage of the Universe, in which the Stückelberg fields are nonlinear and there is neither ghost nor gradient instability. Therefore, the bigravity theory has the healthy massless limit, and cosmology based on it is viable even when the graviton mass is smaller than the Hubble parameter.

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    29
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  • Stability of the early universe in bigravity theory

    Katsuki Aoki, Kei-ichi Maeda, Ryo Namba

    PHYSICAL REVIEW D   92 ( 4 )  2015.08  [Refereed]

     View Summary

    We study the stability of a spherically symmetric perturbation around the flat Friedmann-Lemaitre-Robertson-Walker spacetime in the ghost-free bigravity theory, retaining nonlinearities of the helicity-0 mode of the massive graviton. It has been known that, when the graviton mass is smaller than the Hubble parameter, homogeneous and isotropic spacetimes suffer from the Higuchi-type ghost or the gradient instability against the linear perturbation in the bigravity. Hence, the bigravity theory has no healthy massless limit for cosmological solutions at linear level. In this paper we show that the instabilities can be resolved by taking into account nonlinear effects of the scalar graviton mode for an appropriate parameter space of coupling constants. The growth history in the bigravity can be restored to the result in general relativity in the early stage of the Universe, in which the Stuckelberg fields are nonlinear and there is neither ghost nor gradient instability. Therefore, the bigravity theory has the healthy massless limit, and cosmology based on it is viable even when the graviton mass is smaller than the Hubble parameter.

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    29
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  • Bubble universes with different gravitational constants

    Yu-Ichi Takamizu, Kei-Ichi Maeda

    Physical Review D - Particles, Fields, Gravitation and Cosmology   92 ( 2 )  2015.07

     View Summary

    We argue a scenario motivated by the context of string landscape, where our Universe is produced by a new vacuum bubble embedded in an old bubble and these bubble universes have not only different cosmological constants, but also their own different gravitational constants. We study these effects on the primordial curvature perturbations. In order to construct a model of varying gravitational constants, we use the Jordan-Brans-Dicke theory where different expectation values of scalar fields produce difference of constants. In this system, we investigate the nucleation of the bubble universe and the dynamics of the wall separating two spacetimes. In particular, the primordial curvature perturbation on superhorizon scales can be affected by the wall trajectory as the boundary effect. We show how the gravitational constant in the exterior bubble universe modifies the power spectrum, that provides a peak like a bump feature at a large scale.

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    4
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  • Dark matter in ghost-free bigravity theory: From a galaxy scale to the universe

    Katsuki Aoki, Kei-ichi Maeda

    PHYSICAL REVIEW D   90 ( 12 )  2014.12  [Refereed]

     View Summary

    We study the origin of dark matter based on the ghost-free bigravity theory with twin matter fluids. The present cosmic acceleration can be explained by the existence of graviton mass, while dark matter is required in several cosmological situations (the galactic missing mass, the cosmic structure formation and the cosmic microwave background observation). Assuming that the Compton wavelength of the massive graviton is shorter than a galactic scale, we show the bigravity theory can explain dark matter by twin matter fluid as well as the cosmic acceleration by tuning appropriate coupling constants.

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    22
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  • Cosmic acceleration with a negative cosmological constant in higher dimensions

    Kei-ichi Maeda, Nobuyoshi Ohta

    JOURNAL OF HIGH ENERGY PHYSICS   1406 095 ( 6 )  2014.06  [Refereed]

     View Summary

    We study gravitational theories with a cosmological constant and the Gauss-Bonnet curvature squared term and analyze the possibility of de Sitter expanding spacetime with a constant internal space. We find that there are two branches of the de Sitter solutions: both the curvature of the internal space and the cosmological constant are (1) positive and (2) negative. From the stability analysis, we show that the de Sitter solution of the case (1) is unstable, while that in the case (2) is stable. Namely de Sitter solution in the present system is stable if the cosmological constant is negative. We extend our analysis to the gravitational theories with higher-order Lovelock curvature terms. Although the existence and the stability of the de Sitter solutions are very complicated and highly depend on the coupling constants, there exist stable de Sitter solutions similar to the case (2). We also find de Sitter solutions with Hubble scale much smaller than the scale of a cosmological constant, which may explain a discrepancy between an inflation energy scale and the Planck scale.

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    37
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  • Cosmology in ghost-free bigravity theory with twin matter fluids: The origin of dark matter

    Katsuki Aoki, Kei-ichi Maeda

    PHYSICAL REVIEW D   89 ( 6 )  2014.03  [Refereed]

     View Summary

    We study dynamics of Friedmann-Lemaitre-Robertson-Walker (FLRW) spacetime based on the ghost-free bigravity theory. Assuming the coupling parameters guaranteeing the existence of de Sitter space as well as Minkowski spacetime, we find two stable attractors for spacetime with "twin" dust matter fields: One is de Sitter accelerating universe and the other is matter dominated universe. Although a considerable number of initial data leads to de Sitter universe, we also find matter dominated universe or spacetime with a future singularity for some initial data. The cosmic no-hair conjecture does not exactly hold, but the accelerating expansion can be found naturally. The Lambda-CDM model is obtained as an attractor. We also show that the dark matter component in the Friedmann equation, which originates from another twin matter, can be about 5 times larger than the baryonic matter, by choosing the appropriate coupling constants.

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    19
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  • Stability analysis of inflation with an SU(2) gauge field

    Kei-Ichi Maeda, Kei Yamamoto

    Journal of Cosmology and Astroparticle Physics   2013 ( 12 )  2013.12

     View Summary

    We study anisotropic cosmologies of a scalar field interacting with an SU(2) gauge field via a gauge-kinetic coupling. We analyze Bianchi class A models, which include Bianchi type I, II, VI0, VII0, VIII and IX. The linear stability of isotropic inflationary solution with background magnetic field is shown, which generalizes the known results for U(1) gauge fields. We also study anisotropic inflationary solutions, all of which turn out to be unstable. Then nonlinear stability for the isotropic inflationary solution is examined by numerically investigating the dependence of the late-time behaviour on the initial conditions. We present a number of novel features that may well affect physical predictions and viability of the models. First, in the absence of spatial curvature, strong initial anisotropy leads to a rapid oscillation of gauge field, thwarting convergence to the inflationary attractor. Secondly, the inclusion of spatial curvature destabilizes the oscillatory attractor and the global stability of the isotropic inflation with gauge field is restored. Finally, based on the numerical evidence combined with the knowledge of the eigenvalues for various inflationary solutions, we give a generic lower-bound for the duration of transient anisotropic inflation, which is inversely proportional to the slow-roll parameter. © 2013 IOP Publishing Ltd and Sissa Medialab srl.

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  • Anisotropic universes in the ghost-free bigravity

    Kei-ichi Maeda, Mikhail S. Volkov

    PHYSICAL REVIEW D   87 ( 10 )  2013.05  [Refereed]

     View Summary

    We study Bianchi cosmologies in the ghost-free bigravity theory, assuming both metrics to be homogeneous and anisotropic and of the Bianchi class A, which includes types I, II, VI0, VII0, VIII, and IX. We assume the Universe to contain a radiation and a nonrelativistic matter, with the cosmological term mimicked by the graviton mass. We find that, for generic initial values leading to a late-time self-acceleration, the Universe approaches a state with nonvanishing anisotropies. The anisotropy contribution to the total energy density decreases much slower than in General Relativity and shows the same falloff rate as the energy of a nonrelativistic matter. The solutions show a singularity in the past, and in the Bianchi IX case, the singularity is approached via a sequence of Kasner-like steps, which is characteristic of a chaotic behavior.

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  • Inflationary dynamics with a non-Abelian gauge field

    Kei-Ichi Maeda, Kei Yamamoto

    Physical Review D - Particles, Fields, Gravitation and Cosmology   87 ( 2 )  2013.01  [Refereed]

     View Summary

    We study the dynamics of the homogeneous and isotropic universe with a scalar field and an SU(2) non-Abelian gauge (Yang-Mills) field. The scalar field has an exponential potential and the Yang-Mills field is coupled to the scalar field with an exponential function of the scalar field. We find that the magnetic component of the Yang-Mills field assists acceleration of the cosmic expansion and a power-law inflation becomes possible even if the scalar field potential is steep, which may be expected from some compactification of higher-dimensional unified theories of fundamental interactions. This power-law inflationary solution is a stable attractor in a certain range of coupling parameters. Unlike the case with multiple Abelian gauge fields, the power-law inflationary solution with the dominant electric component is unstable because of the existence of nonlinear coupling of the Yang-Mills field. We also analyze the dynamics for the noninflationary regime, and find several attractor solutions. © 2013 American Physical Society.

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  • Creation of the universe with a stealth scalar field

    Hideki Maeda, Kei-ichi Maeda

    PHYSICAL REVIEW D   86 ( 12 )  2012.12  [Refereed]

     View Summary

    The stealth scalar field is a nontrivial configuration without any backreaction to geometry, which is characteristic for nonminimally coupled scalar fields. Studying the creation probability of the de Sitter universe with a stealth scalar field by Hartle and Hawking's semiclassical method, we show that the effect of the stealth field can be significant. For the class of scalar fields we consider, creation with a stealth field is possible for a discrete value of the coupling constant, and its creation probability is always less than that with a trivial scalar field. However, those creation rates can be almost the same depending on the parameters of the theory. DOI: 10.1103/PhysRevD.86.124045

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    13
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  • Dynamical brane with angles: Collision of the universes

    Kei-ichi Maeda, Kunihito Uzawa

    PHYSICAL REVIEW D   85 ( 8 )  2012.04  [Refereed]

     View Summary

    We present the time-dependent solutions corresponding to the dynamical D-brane with angles in ten-dimensional type II supergravity theories. Our solutions with angles are different from the known dynamical intersecting brane solutions in supergravity theories. Because of our ansatz for fields, all warp factors in the solutions can depend on time. Applying these solutions, we construct cosmological models from those solutions by smearing some dimensions and compactifying the internal space. We find the Friedmann-Lemaitre-Robertson-Walker cosmological solutions with power-law expansion. We also discuss the dynamics of branes based on these solutions. When the spacetime is contracting in ten dimensions, each brane approaches the others as the time evolves. However, for a Dp-brane (p <= 7) without smearing branes, a singularity appears before branes collide. In contrast, the D6-D8-brane system or the smeared D(p - 2) - Dp-brane system with one uncompactified extra dimension can provide an example of colliding branes (and collision of the universes), if they have the same charges.

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  • Accelerating universes in string theory via field redefinition

    Kei-ichi Maeda, Nobuyoshi Ohta, Ryo Wakebe

    EUROPEAN PHYSICAL JOURNAL C   72 ( 3 )  2012.03  [Refereed]

     View Summary

    We study cosmological solutions in the effective heterotic string theory with a alpha'-correction terms in the string frame. It is pointed out that the effective theory has an ambiguity via field redefinition and we analyze generalized effective theories due to this ambiguity. We restrict our analysis to the effective theories which give equations of motion of second order in the derivatives, just as "Galileon" field theory. This class of effective actions contains two free coupling constants. We find de Sitter solutions as well as the power-law expanding universes in our four-dimensional Einstein frame. The accelerated expanding universes are always attractors in the present dynamical system.

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  • Oscillating Bianchi IX universe in Horava-Lifshitz gravity

    Yosuke Misonoh, Kei-ichi Maeda, Tsutomu Kobayashi

    PHYSICAL REVIEW D   84 ( 6 )  2011.09  [Refereed]

     View Summary

    We study a vacuum Bianchi IX universe in the context of Horava-Lifshitz gravity. In particular, we focus on the classical dynamics of the universe and analyze how anisotropy changes the history of the universe. For small anisotropy, we find an oscillating universe as well as a bounce universe just as the case of the Friedmann-Lemaitre-Robertson-Walker spacetime. However, if the initial anisotropy is large, we find the universe which ends up with a big crunch after oscillations if a cosmological constant Lambda is zero or negative. For Lambda > 0, we find a variety of histories of the universe, that is a de Sitter expanding universe after oscillations in addition to the oscillating solution and the previous big crunch solution. This fate of the universe shows sensitive dependence of initial conditions, which is one of the typical properties of a chaotic system. If the initial anisotropy is near the upper bound, we find the universe starting from a big bang and ending up with a big crunch for Lambda <= 0, and a de Sitter expanding universe starting from a big bang for Lambda > 0.

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  • Dynamics of voids and their shapes in redshift space

    Kei-ichi Maeda, Nobuyuki Sakai, Roland Triay

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2011 ( 8 ) 026  2011.08  [Refereed]

     View Summary

    We investigate the dynamics of a single spherical void embedded in a Friedmann-Lemaitre universe, and analyze the void shape in the redshift space. We find that the void in the redshift space appears as an ellipse shape elongated along the line of sight (i.e., an opposite deformation to the Kaiser effect). Applying this result to observed void candidates at the redshift z similar to 1-2, it may provide us with a new method to evaluate the cosmological parameters, in particular the value of a cosmological constant.

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  • AdS black hole solutions in dilatonic Einstein-Gauss-Bonnet gravity

    Kei-ichi Maeda, Nobuyoshi Ohta, Yukinori Sasagawa

    PHYSICAL REVIEW D   83 ( 4 )  2011.02  [Refereed]

     View Summary

    We find that anti-de Sitter (AdS) spacetime with a nontrivial linear dilaton field is an exact solution in the effective action of the string theory, which is described by gravity with the Gauss-Bonnet curvature terms coupled to a dilaton field in the string frame without a cosmological constant. The AdS radius is determined by the spacetime dimensions and the coupling constants of curvature corrections. We also construct the asymptotically AdS black hole solutions with a linear dilaton field numerically. We find these AdS black holes for hyperbolic topology and in dimensions higher than four. We discuss the thermodynamical properties of those solutions. Extending the model to the case with the even-order higher Lovelock curvature terms, we also find the exact AdS spacetime with a nontrivial dilaton. We further find a cosmological solution with a bounce of three-dimensional space and a solitonic solution with a nontrivial dilaton field, which is regular everywhere and approaches an asymptotically AdS spacetime.

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    15
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  • Black Hole Solutions in String Theory

    Kei-ichi Maeda, Masato Nozawa

    PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT   189 ( 189 ) 310 - 350  2011  [Refereed]

     View Summary

    Supersymmetric solutions of supergravity have been of particular importance in the advances of string theory. This article reviews the current status of black hole solutions in higher-dimensional supergravity theories. We discuss primarily the gravitational aspects of supersymmetric black holes and their relatives in various dimensions. Supersymmetric solutions and their systematic derivation are reviewed with prime examples. We also study the stationary or dynamically intersecting branes in ten and eleven-dimensions, which provide a number of interesting black objects via the dimensional reduction and duality transformations.

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  • Innovation to Probe Higher Dimensions through Black Holes: Introduction

    Kei-ichi Maeda, Tetsuya Shiromizu, Takahiro Tanaka

    PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT   189 ( 189 ) 1 - 6  2011  [Refereed]

     View Summary

    Starting with an aspect of motivation to study higher dimensional black holes, we give a brief overview of the whole volume. Finally we give a short note on notations and conventions.

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  • Cosmological rotating black holes in five-dimensional fake supergravity

    Masato Nozawa, Kei-ichi Maeda

    PHYSICAL REVIEW D   83 ( 2 )  2011.01  [Refereed]

     View Summary

    In recent series of papers, we found an arbitrary dimensional, time-evolving, and spatially inhomogeneous solution in Einstein-Maxwell-dilaton gravity with particular couplings. Similar to the supersymmetric case, the solution can be arbitrarily superposed in spite of nontrivial time-dependence, since the metric is specified by a set of harmonic functions. When each harmonic has a single point source at the center, the solution describes a spherically symmetric black hole with regular Killing horizons and the spacetime approaches asymptotically to the Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmology. We discuss in this paper that in 5 dimensions, this equilibrium condition traces back to the first-order "Killing spinor" equation in "fake supergravity" coupled to arbitrary U(1) gauge fields and scalars. We present a five-dimensional, asymptotically FLRW, rotating black-hole solution admitting a nontrivial "Killing spinor," which is a spinning generalization of our previous solution. We argue that the solution admits nondegenerate and rotating Killing horizons in contrast with the supersymmetric solutions. It is shown that the present pseudo-supersymmetric solution admits closed timelike curves around the central singularities. When only one harmonic is time-dependent, the solution oxidizes to 11 dimensions and realizes the dynamically intersecting M2/M2/M2-branes in a rotating Kasner universe. The Kaluza-Klein-type black holes are also discussed.

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  • Professor Hayashi and Four Graduate Students(Dedicated to Professor Chushiro Hayashi)

    Nakamura Takashi, Maeda Kei-ichi, Miyama Shoken, Sasaki Misao

    Butsuri   65 ( 10 ) 795 - 799  2010.10

    CiNii

  • Oscillating universe in Horava-Lifshitz gravity

    Kei-ichi Maeda, Yosuke Misonoh, Tsutomu Kobayashi

    PHYSICAL REVIEW D   82 ( 6 )  2010.09  [Refereed]

     View Summary

    We study the dynamics of isotropic and homogeneous universes in the generalized Horava-Lifshitz gravity, and classify all possible evolutions of vacuum spacetime. In the case without the detailed balance condition, we find a variety of phase structures of vacuum spacetimes depending on the coupling constants as well as the spatial curvature K and a cosmological constant Lambda. A bounce universe solution is obtained for Lambda > 0, K = +/- 1 or Lambda = 0, K = -1, while an oscillation spacetime is found for Lambda >= 0, K = 1, or Lambda < 0, K = +/- 1. We also propose a quantum tunneling scenario from an oscillating spacetime to an inflationary universe, resulting in a macroscopic cyclic universe.

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    39
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  • Dynamical p-branes with a cosmological constant

    Kei-ichi Maeda, Masato Minamitsuji, Nobuyoshi Ohta, Kunihito Uzawa

    Phys.Rev.D82:046007,2010    2010.06

     View Summary

    We present a class of dynamical solutions in a D-dimensional gravitational<br />
    theory coupled to a dilaton, a form field strength, and a cosmological<br />
    constant. We find that for any D due to the presence of a cosmological<br />
    constant, the metric of solutions depends on a quadratic function of the brane<br />
    world volume coordinates, and the transverse space cannot be Ricci flat except<br />
    for the case of 1-branes. We then discuss the dynamics of 1-branes in a<br />
    D-dimensional spacetime. For a positive cosmological constant, 1-brane<br />
    solutions with D&gt;4 approach the Milne universe in the far-brane region. On the<br />
    ...

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  • Black Holes in an Expanding Universe

    Gary W. Gibbons, Kei-ichi Maeda

    PHYSICAL REVIEW LETTERS   104 ( 13 ) 1 - 4  2010.04  [Refereed]

     View Summary

    An exact solution representing black holes in an expanding universe is found. The black holes are maximally charged and the universe is expanding with arbitrary equation of state (P = w rho with -1 &lt;= for all w &lt;= 1). It is an exact solution of the Einstein-scalar-Maxwell system, in which we have two Maxwell-type U(1) fields coupled to the scalar field. The potential of the scalar field is an exponential. We find a regular horizon, which depends on one parameter [the ratio of the energy density of U(1) fields to that of the scalar field]. The horizon is static because of the balance on the horizon between gravitational attractive force and U(1) repulsive force acting on the scalar field. We also calculate the black hole temperature.

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  • Supersymmetric intersecting branes on the waves

    Kei-ichi Maeda, Nobuyoshi Ohta, Makoto Tanabe, Ryo Wakebe

    JOURNAL OF HIGH ENERGY PHYSICS   1004:013 ( 4 )  2010.04  [Refereed]

     View Summary

    We construct a general family of supersymmetric solutions in time- and space-dependent wave backgrounds in general supergravity theories describing single and intersecting p-branes embedded into time-dependent dilaton-gravity plane waves of an arbitrary (isotropic) profile, with the brane world-volume aligned parallel to the propagation direction of the wave. We discuss how many degrees of freedom we have in the solutions. We also propose that these solutions can be used to describe higher-dimensional time-dependent "black holes", and discuss their property briefly.

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  • Black hole in the expanding universe from intersecting branes

    Kei-ichi Maeda, Masato Nozawa

    PHYSICAL REVIEW D   81 ( 4 )  2010.02  [Refereed]

     View Summary

    We study physical properties and global structures of a time-dependent, spherically symmetric solution obtained via the dimensional reduction of intersecting M-branes. We find that the spacetime describes a maximally charged black hole which asymptotically tends to the Friedmann-Lemaitre-Robertson-Walker universe filled by a stiff matter. The metric solves the field equations of the Einstein-Maxwell-dilaton system, in which four Abelian gauge fields couple to the dilation with different coupling constants. The spacetime satisfies the dominant energy condition and is characterized by two parameters, Q and tau, related to the Maxwell charge and the relative ratio of black-hole horizon radii, respectively. In spite of the nontrivial time dependence of the metric, it turns out that the black-hole event horizon is a Killing horizon. This unexpected symmetry may be ascribed to the fact that the 11-dimensional brane configurations are supersymmetric in the static limit. Finally, combining with laws of the trapping horizon, we discuss the thermodynamic properties of the black hole. It is shown that the horizon possesses a nonvanishing temperature, contrary to the extremal Reissner-Nordstrom solution.

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  • Black hole solutions in string theory with Gauss-Bonnet curvature correction

    Kei-ichi Maeda, Nobuyoshi Ohta, Yukinori Sasagawa

    PHYSICAL REVIEW D   80 ( 10 )  2009.11  [Refereed]

     View Summary

    We present the black hole solutions and analyze their properties in the superstring effective field theory with the Gauss-Bonnet curvature correction terms. We find qualitative differences in our results from those obtained in the truncated model in the Einstein frame. The main difference in our model from the truncated one is that the existence of a turning point in the mass-area curve, the mass-entropy curve, and the mass-temperature curve in five and higher dimensions, where we expect a change of stability. We also find a mass gap in our model, where there is no black hole solution. In five dimensions, there exists a maximum black hole temperature and the temperature vanishes at the minimum mass, which is not found in the truncated model.

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  • Black hole solutions in string theory with Gauss-Bonnet curvature correction

    Kei-ichi Maeda, Nobuyoshi Ohta, Yukinori Sasagawa

    PHYSICAL REVIEW D   80 ( 10 )  2009.11  [Refereed]

     View Summary

    We present the black hole solutions and analyze their properties in the superstring effective field theory with the Gauss-Bonnet curvature correction terms. We find qualitative differences in our results from those obtained in the truncated model in the Einstein frame. The main difference in our model from the truncated one is that the existence of a turning point in the mass-area curve, the mass-entropy curve, and the mass-temperature curve in five and higher dimensions, where we expect a change of stability. We also find a mass gap in our model, where there is no black hole solution. In five dimensions, there exists a maximum black hole temperature and the temperature vanishes at the minimum mass, which is not found in the truncated model.

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    68
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  • The Bernstein conjecture, minimal cones and critical dimensions

    Gary W. Gibbons, Kei-Ichi Maeda, Umpei Miyamoto

    CLASSICAL AND QUANTUM GRAVITY   26 ( 18 )  2009.09  [Refereed]

     View Summary

    Minimal surfaces and domain walls play important roles in various contexts of spacetime physics as well as material science. In this paper, we first review the Bernstein conjecture, which asserts that a plane is the only globally well-defined solution of the minimal surface equation which is a single valued graph over a hyperplane in flat spaces, and its failure in higher dimensions. Then, we review how minimal cones in four- and higher-dimensional spacetimes, which are curved and even singular at the apex, may be used to provide counterexamples to the conjecture. The physical implications of these counterexamples in curved spacetimes are discussed from various points of view, ranging from classical general relativity, brane physics and holographic models of fundamental interactions.

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  • Measurement of the Kerr spin parameter by observation of a compact object's shadow

    Kenta Hioki, Kei-ichi Maeda

    PHYSICAL REVIEW D   80 ( 2 )  2009.07  [Refereed]

     View Summary

    A black hole casts a shadow as an optical appearance because of its strong gravitational field. We study how to determine the spin parameter and the inclination angle by observing the apparent shape of the shadow, which is distorted mainly by those two parameters. Defining some observables characterizing the apparent shape (its radius and distortion parameter), we find that the spin parameter and inclination angle of a Kerr black hole can be determined by the observation. This technique is also extended to the case of a Kerr naked singularity.

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  • Dynamics of intersecting brane systems - Classification and their applications

    Kei-ichi Maeda, Nobuyoshi Ohta, Kunihito Uzawa

    JOURNAL OF HIGH ENERGY PHYSICS   0906:051 ( 6 )  2009.06  [Refereed]

     View Summary

    We present dynamical intersecting brane solutions in higher-dimensional gravitational theory coupled to dilaton and several forms. Assuming the forms of metric, form fields, and dilaton field, we give a complete classification of dynamical intersecting brane solutions with/without M-waves and Kaluza-Klein monopoles in eleven-dimensional super-gravity. We apply these solutions to cosmology and black holes. It is shown that these give FRW cosmological solutions and in some cases Lorentz invariance is broken in our world. If we regard the bulk space as our universe, we may interpret them as black holes in the expanding universe. We also discuss lower-dimensional effective theories and point out naive effective theories may give us some solutions which are inconsistent with the higher-dimensional Einstein equations.

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    44
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  • Supersymmetric intersecting branes in time-dependent backgrounds

    Kei-ichi Maeda, Nobuyoshi Ohta, Makoto Tanabea, Ryo Wakebea

    JOURNAL OF HIGH ENERGY PHYSICS   0906:036 ( 6 )  2009.06  [Refereed]

     View Summary

    We construct a fairy general family of supersymmetric solutions in time- and space-dependent backgrounds in general supergravity theories. One class of the solutions are intersecting brane solutions with factorized form of time- and space-dependent metrics, the second class are brane solutions in pp-wave backgrounds carrying spacetime-dependence, and the final class are the intersecting branes with more nontrivial spacetime-dependence, and their intersection rules are given. Physical properties of these solutions are discussed, and the relation to existing literature is also briefly mentioned. The number of remaining supersymmetries are identified for various configurations including single branes, D1-D5, D2-D6-branes with nontrivial dilaton, and their possible dual theories are briefly discussed.

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  • Attractor universe in the scalar-tensor theory of gravitation

    Kei-ichi Maeda, Yasunori Fujii

    PHYSICAL REVIEW D   79 ( 8 )  2009.04  [Refereed]

     View Summary

    In the scalar-tensor theory of gravitation it seems nontrivial to establish if solutions of the cosmological equations in the presence of a cosmological constant (or a vacuum energy) behave as attractors independently of the initial values. We develop a general formulation in terms of two-dimensional phase space, mainly according to the Brans-Dicke model requiring the scalar field decoupled from the matter Lagrangian in the Jordan frame. We show that there are two kinds of fixed points, one of which is an attractor depending on the coupling constant and equation of state. We find that the static universe in the Jordan frame is an attractor in the presence of a cosmological constant for some range of the coupling constant. We extend our analysis to a power-law potential, finding a new type of power-law inflation caused by the coupling to the matter fluid, also as an attractor.

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    27
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  • Black hole-black string phase transitions from hydrodynamics

    Kei-ichi Maeda, Umpei Miyamoto

    JOURNAL OF HIGH ENERGY PHYSICS   0903:066 ( 3 )  2009.03  [Refereed]

     View Summary

    We discuss the phase transitions between three states of a plasma fluid (plasma ball, uniform plasma tube, and non-uniform plasma tube), which are dual to the corresponding finite energy black objects (black hole, uniform black string, and non-uniform black string) localized in an asymptotically locally AdS space. Adopting the equation of state for the fluid obtained by the Scherk-Schwarz compactification of a conformal field theory, we obtain axisymmetric static equilibrium states of the plasma fluid and draw the phase diagrams with their thermodynamical quantities. By use of the fluid/gravity correspondence, we predict the phase diagrams of the AdS black holes and strings on the gravity side. The thermodynamic phase diagrams of the AdS black holes and strings show many similarities to those of the black hole-black string system in a Kaluza-Klein vacuum. For instance, the critical dimension for the smooth transition from the uniform to non-uniform strings is the same as that in the Kaluza-Klein vacuum in the canonical ensemble. The analysis in this paper may provide a holographic understanding of the relation between the Rayleigh-Plateau and Gregory-Laflamme instabilities via the fluid/gravity correspondence.

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  • Can higher curvature corrections cure the singularity problem in f(R) gravity?

    Tsutomu Kobayashi, Kei-ichi Maeda

    PHYSICAL REVIEW D   79 ( 2 )  2009.01  [Refereed]

     View Summary

    Although f(R) modified gravity models can be made to satisfy solar system and cosmological constraints, it has been shown that they have the serious drawback of the nonexistence of stars with strong gravitational fields. In this paper, we discuss whether or not higher curvature corrections can remedy the nonexistence consistently. The following problems are shown to arise as the costs one must pay for the f(R) models that allow for neutrons stars: (i) the leading correction must be fine-tuned to have the typical energy scale mu less than or similar to 10(-19) GeV, which essentially comes from the free fall time of a relativistic star; (ii) the leading correction must be further fine-tuned so that it is not given by the quadratic curvature term. The second problem is caused because there appears an intermediate curvature scale, and laboratory experiments of gravity will be under the influence of higher curvature corrections. Our analysis thus implies that it is a challenge to construct viable f(R) models without very careful and unnatural fine-tuning.

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  • One-loop corrections to scalar and tensor perturbations during inflation in stochastic gravity

    Yuko Urakawa, Kei-ichi Maeda

    PHYSICAL REVIEW D   78 ( 6 )  2008.09

     View Summary

    Based on the stochastic gravity, we study the loop corrections to the scalar and tensor perturbations during inflation. Since the loop corrections to scalar perturbations suffer infrared divergence, we consider the IR regularization to obtain the finite value. We find that the loop corrections to the scalar perturbations are amplified by the e-folding; in other words there appears the logarithmic correction, just as discussed by M. Sloth et al. On the other hand, we find that the tensor perturbations do not suffer from infrared divergence.

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  • Relativistic stars in f(R) gravity, and absence thereof

    Tsutomu Kobayashi, Kei-ichi Maeda

    PHYSICAL REVIEW D   78 ( 6 )  2008.09

     View Summary

    Several f(R) modified gravity models have been proposed which realize the correct cosmological evolution and satisfy solar system and laboratory tests. Although nonrelativistic stellar configurations can be constructed, we argue that relativistic stars cannot be present in such f(R) theories. This problem appears due to the dynamics of the effective scalar degree of freedom in the strong gravity regime. Our claim thus raises doubts on the viability of f(R) models.

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  • Liquid bridges and black strings in higher dimensions

    Umpei Miyamoto, Kei-ichi Maeda

    PHYSICS LETTERS B   664 ( 1-2 ) 103 - 106  2008.06  [Refereed]

     View Summary

    Analyzing a capillary minimizing problem for a higher-dimensional extended fluid, we find that there exist startling similarities between the black hole-black string system (the Gregory-Laflamme instability) and the liquid drop-liquid bridge system (the Rayleigh-Plateau instability), which were first suggested by a perturbative approach. In the extended fluid system, we confirm the existence of the critical dimension above which the non-uniform bridge (NUB, i.e., Delaunay unduloid) serves as the global minimizer of surface area. We also find a variety of phase structures (one or two cusps in the volume-area phase diagram) near the critical dimension. Applying a catastrophe theory, we predict that in the 9-dimensional (9D) space and below, we have the first order transition from a uniform bridge (UB) to a spherical drop (SD), while in the 10D space and above, we expect the transition such that UB -&gt; NUB -&gt; SD. This gives an important indication for a transition in the black hole-black string system. (C) 2008 Elsevier B.V. All rights reserved.

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  • Entropy function and universality of entropy-area relation for small black holes

    Rong-Gen Cai, Chiang-Mei Chen, Kei-Ichi Maeda, Nobuyoshi Ohta, Da-Wei Pang

    PHYSICAL REVIEW D   77 ( 6 )  2008.03  [Refereed]

     View Summary

    We discuss the entropy-area relation for the small black holes with higher curvature corrections by using the entropy function formalism and field redefinition method. We show that the entropy S-BH of the small black hole is proportional to its horizon area A. In particular, we find a universal result that S-BH = A/2G, the ratio is 2 times of Bekenstein-Hawking entropy-area formula in many cases of physical interest. In four dimensions, the universal relation is always true irrespective of the coefficients of the higher-order terms if the dilaton couplings are the same, which is the case for string effective theory, while in five dimensions, the relation again holds irrespective of the overall coefficient if the higher-order corrections are in the GB combination. We also discuss how this result generalizes to known physically interesting cases with Lovelock correction terms in various dimensions, and possible implications of the universal relation.

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  • Cosmological density fluctuations in stochastic gravity: Formalism and linear analysis

    Yuko Urakawa, Kei-ichi Maeda

    PHYSICAL REVIEW D   77 ( 2 )  2008.01  [Refereed]

     View Summary

    We study primordial perturbations generated from quantum fluctuations of an inflaton based on the formalism of stochastic gravity. Integrating out the degree of freedom of the inflaton field, we analyze the time evolution of the correlation function of the curvature perturbation at tree level and compare it with the prediction made by the gauge-invariant linear perturbation theory. We find that our result coincides with that of the gauge-invariant perturbation theory if the e-folding from the horizon-crossing time is smaller than some critical value (similar to vertical bar slow-roll parameter vertical bar(-1)), which is the case for the scales of the observed cosmological structures. However, in the limit of the superhorizon scale, we find a discrepancy in the curvature perturbation, which suggests that we should include the longitudinal part of the gravitational field in the quantization of a scalar field even in stochastic gravity.

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  • Collision of domain walls and creation of matter in brane world

    Kei-ichi Maeda

    PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT   172 ( 172 ) 90 - 99  2008  [Refereed]

     View Summary

    We study collision of two domain walls in five-dimensional (5D) spacetime and creation of matter fields. This may provide the reheating mechanism in cosmological models based on a colliding-brane scenario such as the ekpyrotic (or cyclic) universe.
    We first analyze the dynamics of colliding domain walls both in 5D Minkowski background spacetime and in asymptotic AdS spacetime including self-gravity. We find that multiple bounces appear at collision. In the case with gravity, we find that a spacelike curvature singularity is formed in the bulk, but it is covered by a horizon.
    Next we analyze production of particles at collision of two domain walls. For a scalar 0 where g is a field, the energy density of created particles is evaluated as rho approximate to 20(g)(-4) Nb m(Phi)(4) coupling constant of particles to a domain-wall scalar field, Nb is the number of bounces at the collision and m Phi is a fundamental mass scale of the domain wall. We also study the behaviour, of 5D fermions localized on domain walls, when two walls collide in a 5D Minkowski background spacetime. For kappa = 0 mode, we find that most fermions are localized on both branes as a whole even after collision. However, how much fermions are localized on which brane depends sensitively on the incident velocity and the coupling constants.

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  • Gravitational wave signals from a chaotic system: A point mass with a disk

    Kenta Kiuchi, Hiroko Koyama, Kei-ichi Maeda

    PHYSICAL REVIEW D   76 ( 2 )  2007.07  [Refereed]

     View Summary

    We study gravitational waves from a particle moving around a system of a point mass with a disk in Newtonian gravitational theory. A particle motion in this system can be chaotic when the gravitational contribution from a surface density of a disk is comparable with that from a point mass. In such an orbit, we sometimes find that there appears a phase in which particle motion becomes nearly regular (so-called "stagnant motion" or stickiness) for a finite time interval between more strongly chaotic phases. To study how these different chaotic behaviors affect observation of gravitational waves, we investigate a correlation of the particle motion and the waves. We find that such a difference in chaotic motions reflects on the wave forms and energy spectra. The character of the waves in the stagnant motion is quite different from that either in a regular motion or in a more strongly chaotic motion. This suggests that we may make a distinction between different chaotic behaviors of the orbit via the gravitational waves.

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    11
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  • Fermions on colliding branes

    Gary Gibbons, Kei-ichi Maeda, Yu-ichi Takamizu

    PHYSICS LETTERS B   647 ( 1 ) 1 - 7  2007.03  [Refereed]

     View Summary

    We study the behaviour of five-dimensional fermions localized on branes, which we describe by domain walls, when two parallel branes collide in a five-dimensional Minkowski background spacetime. We find that most fermions are localized on both branes as a whole even after collision. However, how much fermions are localized on which brane depends sensitively on the incident velocity and the coupling constants unless the fermions exist on both branes. (c) 2007 Elsevier B.V. All rights reserved.

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    28
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  • Dynamics of colliding branes and black brane production

    Yu-ichi Takamizu, Hideaki Kudoh, Kei-ichi Maeda

    PHYSICAL REVIEW D   75 ( 6 ) 1 - 5  2007.03  [Refereed]

     View Summary

    We study the dynamics of colliding domain walls including self-gravity. The initial data is set up by applying a Bogomol'nyi-Prasad-Sommerfield (BPS) domain wall in five-dimensional supergravity, and we evolve the system determining the final outcome of collisions. After a collision, a spacelike curvature singularity covered by a horizon is formed in the bulk, resulting in a black brane with trapped domain walls. This is a generic consequence of collisions, except for nonrelativistic weak field cases, in which the walls pass through one another or multiple bounces take place without singularity formation. These results show that incorporating the self-gravity drastically changes a naive picture of colliding branes.

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    12
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  • Supersymmetric rotating black hole in a compactified spacetime

    Kei-ichi Maeda, Nobuyoshi Ohta, Makoto Tanabe

    PHYSICAL REVIEW D   74 ( 10 ) 1 - 7  2006.11  [Refereed]

     View Summary

    We construct a supersymmetric rotating black hole with asymptotically flat four-dimensional spacetime times a circle, by superposing an infinite number of BMPV black hole solutions at the same distance in one direction. The near-horizon structure is the same as that of the five-dimensional BMPV black hole. The rotation of this black hole can exceed the Kerr bound in general relativity (q equivalent to a/G(4)M=1), if the size is small.

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    10
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  • Inflation from superstring and M-theory compactification with higher order corrections. II. Case of quartic Weyl terms

    Kenta Akune, Kei-ichi Maeda, Nobuyoshi Ohta

    PHYSICAL REVIEW D   73 ( 10 ) 1 - 20  2006.05  [Refereed]

     View Summary

    We present a detailed study of inflationary solutions in M theory with higher order quantum corrections. We first exhaust all exact and asymptotic solutions of exponential and power-law expansions in this theory with quartic curvature corrections, and then perform a linear perturbation analysis around fixed points for the exact solutions in order to see which solutions are more generic and give interesting cosmological models. We find an interesting solution in which the external space expands exponentially and the internal space is static both in the original and Einstein frames. Furthermore, we perform a numerical calculation around this solution and find numerical solutions which give enough e-foldings. We also briefly summarize similar solutions in type II superstrings.

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    58
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  • Collision of domain walls in asymptotically anti-de Sitter spacetime

    Yu-ichi Takamizu, Kei-ichi Maeda

    PHYSICAL REVIEW D   73 ( 10 ) 1 - 11  2006.05  [Refereed]

     View Summary

    We study collision of two domain walls in five-dimensional asymptotically anti-de Sitter spacetime. This may provide the reheating mechanism of an ekpyrotic (or cyclic) brane universe, in which two Bogomol'nyi-Prasad-Sommerfield branes collide and evolve into a hot big bang universe. We evaluate a change of scalar field making the domain wall and can investigate the effect of a negative cosmological term in the bulk to the collision process and the evolution of our universe.

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    22
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  • Stationary spacetime from intersecting M-branes

    Makoto Tanabe, Kei-Ichi Maeda

    Journal of Physics: Conference Series   33 ( 1 ) 393 - 398  2006.04

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    We study a stationary "black" brane in M/superstring theory. Assuming BPS-type relations between the first-order derivatives of metric functions, we present general stationary black brane solutions with a traveling wave for the Einstein equations in D-dimensions. The solutions are given by a few independent harmonic equations (and plus the Poisson equation). General solutions are constructed by superposition of a complete set of those harmonic functions. Using the hyperspherical coordinate system, we explicitly give the solutions in 11-dimensional M theory for the case with M2⊥M5 intersecting branes and a traveling wave. Compactifying these solutions into five dimensions, we show that these solutions include the BMPV black hole and the Brinkmann wave solution. We also find new solutions similar to the Brinkmann wave. We prove that the solutions preserve the 1/8 supersymmetry if the gravi-electromagnetic field ℱij, which is a rotational part of gravity, is self-dual. We also discuss non-spherical "black" objects (e.g., a ring topology and an elliptical shape) by use of other curvilinear coordinates. © 2006 IOP Publishing Ltd.

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  • Stationary spacetime from intersecting M-branes

    Makoto Tanabe, Kei-ichi Maeda

    THIRD 21COE SYMPOSIUM: ASTROPHYSICS AS INTERDISCIPLINARY SCIENCE   31   215 - +  2006  [Refereed]

     View Summary

    We study a stationary "black" brane in M/superstring theory. Assuming BPS-type relations between the first-order derivatives of metric functions, we present general stationary black brane solutions with a traveling wave for the Einstein equations in D-dimensions. The solutions are given by a few independent harmonic equations (and plus the Poisson equation). General solutions are constructed by superposition of a complete set of those harmonic functions. We prove that the solutions preserve the 1/8 supersymmetry if the gravi-electromagnetic field F-ij, which is a rotational part of gravity, is self-dual.

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  • Creation of a brane world with a bulk scalar field

    Koh-suke Aoyanagi, Kei-ichi Maeda

    THIRD 21COE SYMPOSIUM: ASTROPHYSICS AS INTERDISCIPLINARY SCIENCE   31   219 - +  2006  [Refereed]

     View Summary

    We investigate a creation of a brane world with a bulk scalar field. We consider an exponential potential of a bulk scalar field; V(phi) proportional to exp(-2 beta phi), where beta is the parameter of the theory. This model is based on a supersymmetric theory, and includes Randall-Sundrum model (beta = 0) and the 5-dimensional effective model of the Horva-Witten theory (beta = 1). We show that for this potential a brane instanton is constructed only when a curvature of a brane vanishes, that is, the brane is flat. We construct an instanton with two branes and a singular instanton with a single brane. The Euclidean action of the singular instanton solution is finite if beta(2) &gt; 2/3. We also calculate perturbations of the action around a singular instanton solution in order to show that the singular instanton is well-defined.

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  • Chaos of Yang-Mills field in Bianchi spacetimes

    Yoshida Jin, Kei-Ichi Maeda

    The Tenth Marcel Grossmann Meeting: On Recent Developments in Theoretical and Experimental General Relativity, Gravitation and Relativistic Field Theories   3   1877 - 1882  2006.01

     View Summary

    Studying Yang-Mills field in Bianchi spacetime, we find that Yang-Mills field shows chaotic behaviors in the Einstein-Yang-Mills (EYM) system. We also analyze a multiplicative effect by two types of chaos, that is, chaos found with Yang-Mills field and that found in Bianchi IX spacetime. Although we find that chaotic behavior of Yang- Mills field in such a system, two types do not coexist, resulting that no enhancement is obtained.

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  • Cosmological coevolution of Yang-Mills fields and perfect fluids - art. no. 1035012

    JD Barrow, Y Jin, K Maeda

    PHYSICAL REVIEW D   72 ( 10 ) 1 - 13  2005.11  [Refereed]

     View Summary

    We study the coevolution of Yang-Mills fields and perfect fluids in Bianchi type I universes. We investigate numerically the evolution of the universe and the Yang-Mills fields during the radiation and dust eras of a universe that is almost isotropic. The Yang-Mills field undergoes small amplitude chaotic oscillations, as do the three expansion scale factors which are also displayed by the expansion scale factors of the universe. The results of the numerical simulations are interpreted analytically and compared with past studies of the cosmological evolution of magnetic fields in radiation and dust universes. We find that, whereas magnetic universes are strongly constrained by the microwave background anisotropy, Yang-Mills universes are principally constrained by primordial nucleosynthesis but the bound is comparatively weak with Omega(YM)&lt; 0.105 Omega(rad).

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    12
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  • The fate of a five-dimensional rotating black hole via hawking radiation

    H Nomura, S Yoshida, M Tanabe, K Maeda

    PROGRESS OF THEORETICAL PHYSICS   114 ( 3 ) 707 - 712  2005.09  [Refereed]

     View Summary

    We study the evolution of a five-dimensional rotating black hole emitting scalar field radiation via the Hawking process for arbitrary initial values of the two rotation parameters a and b. It is found that any such black hole whose initial rotation parameters are both nonzero evolves toward an asymptotic state a/M-l/2 = b/M-1/2 = const(not equal 0), where this constant is independent of the initial values of a and b.

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    34
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  • Energy extraction from higher dimensional black holes and black rings

    M Nozawa, K Maeda

    PHYSICAL REVIEW D   71 ( 8 ) 1 - 11  2005.04  [Refereed]

     View Summary

    We analyze the energy extraction by the Penrose process in higher dimensions. Our result shows the efficiency of the process from higher dimensional black holes and black rings can be rather high compared with that in the four-dimensional Kerr black hole. In particular, if one rotation parameter vanishes, the maximum efficiency becomes infinitely large because the angular momentum is not bounded from above. We also apply a catastrophe theory to analyze the stability of black rings. It indicates a branch of black rings with higher rotational energy is unstable, which should be a different type of instability from the Gregory-Laflamme one.

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    40
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  • Chaos of Yang-Mills field in class A Bianchi spacetimes

    Y Jin, K Maeda

    PHYSICAL REVIEW D   71 ( 6 ) 1 - 13  2005.03  [Refereed]

     View Summary

    Studying the Yang-Mills field and the gravitational field in class A Bianchi spacetimes, we find that chaotic behavior appears in the late phase (the asymptotic future). In this phase, the Yang-Mills field behaves as that in Minkowski spacetime, in which we can understand it by a potential picture, except for types VIII and IX. At the same time, in the initial phase (near the initial singularity), we numerically find that the behavior seems to approach the Kasner solution. However, we show that the Kasner circle is unstable and the Kasner solution is not an attractor. From an analysis of stability and numerical simulation, we find a Mixmaster-like behavior in Bianchi I spacetime. Although this result may provide a counterexample to the Belinskii, Khalatnikov, and Lifshitz (BKL) conjecture, we show that the BKL conjecture is still valid in Bianchi IX spacetime. We also analyze a multiplicative effect of two types of chaos, that is, chaos with the Yang-Mills field and that in vacuum Bianchi IX spacetime. Two types of chaos seem to coexist in the initial phase. However, the effect due to the Yang-Mills field is much smaller than that of the curvature term.

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    13
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  • Inflation from superstring and M-theory compactification with higher order corrections

    K Maeda, N Ohta

    PHYSICAL REVIEW D   71 ( 6 ) 1 - 27  2005.03  [Refereed]

     View Summary

    We study time-dependent solutions in M and superstring theories with higher-order corrections. We first present general field equations for theories of Lovelock type with stringy corrections in arbitrary dimensions. We then exhaust all exact and asymptotic solutions of exponential and power-law expansions in the theory with Gauss-Bonnet terms relevant to heterotic strings and in the theories with quartic corrections corresponding to the M theory and type II superstrings. We discuss interesting inflationary solutions that can generate enough e foldings in the early universe.

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    102
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  • Collision of domain walls and reheating of the brane universe

    Y Takamizu, K Maeda

    PHYSICAL REVIEW D   70 ( 12 ) 1 - 10  2004.12  [Refereed]

     View Summary

    We study particle production at the collision of two domain walls in 5-dimensional Minkowski spacetime. This may provide the reheating mechanism of an ekpyrotic (or cyclic) brane universe, in which two BPS branes collide and evolve into a hot big bang universe. We evaluate a production rate of particles confined to the domain wall. The energy density of created particles is given as rhoapproximate to20 (g) over bar (4)N(b)m(eta)(4) where (g) over bar is a coupling constant of particles to a domain-wall scalar field, N-b is the number of bounces at the collision and m(eta) is the fundamental mass scale of the domain wall. It does not depend on the width d of the domain wall, although the typical energy scale of created particles is given by omegasimilar to1/d. The reheating temperature is evaluated as T(R)approximate to0.88 (g) over barN(b)(1/4). In order to have the baryogenesis at the electro-weak energy scale, the fundamental mass scale is constrained as m(eta)greater than or similar to1.1x10(7) GeV for (g) over bar similar to10(-5).

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    33
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  • Creation of a brane world with a Gauss-Bonnet term

    K Aoyanagi, K Maeda

    PHYSICAL REVIEW D   70 ( 12 ) 1 - 9  2004.12  [Refereed]

     View Summary

    Here we study the creation of a brane world using an instanton solution with Hartle-Hawking's no-boundary approach. We analyze brane models with a Gauss-Bonnet term in a bulk spacetime. The curvature of 3-brane is assumed to be closed, flat, or open. We construct instanton solutions with branes for our models, and calculate the value of the actions to discuss the initial state of a brane universe.

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    10
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  • Domain wall dynamics in brane world and nonsingular cosmological models

    N Okuyama, K Maeda

    PHYSICAL REVIEW D   70 ( 6 ) 1 - 12  2004.09  [Refereed]

     View Summary

    We study brane cosmology as 4D (four-dimensional) domain-wall dynamics in 5D bulk spacetime. For a generic 5D bulk with 3D maximal symmetry, we derive the equation of motion of a domain wall and find that it depends on mass function of the bulk spacetime, and the energy-momentum conservation in a domain wall is affected by a lapse function in the bulk. Especially, for a bulk spacetime with nontrivial lapse function, energy of matter field on the domain wall goes out or comes in from the bulk spacetime. Applying our result to the case with SU(2) gauge bulk field, we obtain a singularity-free universe in brane world scenario, that is, not only a big bang initial singularity of the brane is avoided but also a singularity in a 5D bulk does not exist.

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    8
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  • Gravitational waves from a chaotic dynamical system

    K Kiuchi, K Maeda

    PHYSICAL REVIEW D   70 ( 6 ) 1 - 8  2004.09  [Refereed]

     View Summary

    To investigate how chaos affects gravitational waves, we study the gravitational waves from a spinning test particle moving around a Kerr black hole, which is a typical chaotic system. To compare the result with those in a nonchaotic dynamical system, we also analyze a spinless test particle, whose orbit can be complicated in the Kerr back ground although the system is integrable. We estimate the emitted gravitational waves by the multipole expansion of a gravitational field. We find a striking difference in the energy spectra of the gravitational waves. The spectrum for a chaotic orbit of a spinning particle contains various frequencies, while some characteristic frequencies appear in the case of a spinless particle.

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    30
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  • Inflation from M-theory with fourth-order corrections and large extra dimensions

    K Maeda, N Ohta

    PHYSICS LETTERS B   597 ( 3-4 ) 400 - 407  2004.09  [Refereed]

     View Summary

    We study inflationary solutions in the M-theory. Including the fourth-order curvature correction terms, we find three generalized de Sitter solutions, in which our 3-space expands exponentially. Taking one of the solutions, we propose an inflationary scenario of the early universe. This provides us a natural explanation for large extra dimensions in a brane world, and suggests some connection between the 60 e-folding expansion of inflation and TeV gravity based on the large extra dimensions. (C) 2004 Elsevier B.V. All rights reserved.

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    92
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  • Regular and black hole skyrmions with axisymmetry

    N Sawado, N Shiiki, K Maeda, T Torii

    GENERAL RELATIVITY AND GRAVITATION   36 ( 6 ) 1361 - 1371  2004.06  [Refereed]

     View Summary

    It has been known that a B=2 skyrmion is axially symmetric. We consider the Skyrme model coupled to gravity and obtain static axially symmetric regular and black hole solutions numerically. Computing the energy density of the skyrmion, we discuss the effect of gravity to the energy density and baryon density of the skyrmion.

  • Creation of a brane world with a Gauss-Bonnet term

    Koh-suke Aoyanagi, Kei-ichi Maeda

    Physical Review D - Particles, Fields, Gravitation and Cosmology   70 ( 12 ) 10  2004

     View Summary

    Here we study the creation of a brane world using an instanton solution with Hartle-Hawking’s no-boundary approach. We analyze brane models with a Gauss-Bonnet term in a bulk spacetime. The curvature of 3-brane is assumed to be closed, flat, or open. We construct instanton solutions with branes for our models, and calculate the value of the actions to discuss the initial state of a brane universe. © 2004 The American Physical Society.

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    10
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  • Dilaton dynamics in (A)dS(5)xS(5)

    K Uzawa, K Maeda

    PHYSICAL REVIEW D   68 ( 8 ) 1 - 16  2003.10  [Refereed]

     View Summary

    We investigate a stabilization of extra dimensions in a ten-dimensional Kaluza-Klein theory and type IIB supergravity. We assume (A)dS(5)xS(5) compactification, and calculate quantum effects to find an effective potential for the radius of internal space. The effective potential has a minimum, and if the universe is created on the top of the potential hill, the universe evolves from dS(5) to AdS(5) after exponential expansion. The internal space S-5 stays small and its radius becomes constant. Our model in type IIB supergravity contains the 4-form gauge field with a classical vacuum expectation value, which is the role of a ten-dimensional cosmological constant. If the universe evolves into anti-de Sitter, the five-dimensional Randall-Sundrum setup with a stabilized dilaton is obtained from the type IIB supergravity model.

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  • Stability analysis of black holes via a catastrophe theory and black hole thermodynamics in generalized theories of gravity

    T Tamaki, T Torii, K Maeda

    PHYSICAL REVIEW D   68 ( 2 ) 1 - 10  2003.07  [Refereed]

     View Summary

    We perform a linear perturbation analysis for black hole solutions with a "massive" Yang-Mills field (the Proca field) in Brans-Dicke theory and find that the results are quite consistent with those via catastrophe theory where thermodynamic variables play an intrinsic role. Based on this observation, we show the general relation between these two methods in generalized theories of gravity which are conformally related to the Einstein-Hilbert action.

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    24
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  • Effective gravitational equations on a brane world with induced gravity

    K Maeda, S Mizuno, T Torii

    PHYSICAL REVIEW D   68 ( 2 ) 1 - 8  2003.07  [Refereed]

     View Summary

    We present the effective equations to describe the four-dimensional gravity of a brane world, assuming that a five-dimensional bulk spacetime satisfies the Einstein equations and gravity is confined on the Z(2) symmetric brane. Applying this formalism, we study the induced-gravity brane model first proposed by Dvali, Gabadadze, and Porrati. In a generalization of their model, we show that an effective cosmological constant on the brane can be extremely reduced in contrast with the case of the Randall-Sundrum model even if a bulk cosmological constant and a brane tension are not fine tuned.

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    131
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  • Five-dimensional black hole and particle solution with a non-Abelian gauge field

    N Okuyama, K Maeda

    PHYSICAL REVIEW D   67 ( 10 ) 1 - 17  2003.05  [Refereed]

     View Summary

    We study the five-dimensional Einstein-Yang-Mills system with a cosmological constant. Assuming a spherically symmetric spacetime, we find a new analytic black hole solution, which approaches asymptotically "quasi-Minkowski," "quasi-anti-de Sitter," or "quasi-de Sitter" spacetime depending on the sign of the cosmological constant. Since there is no singularity except for the origin that is covered by an event horizon, we regard it as a localized object. This solution corresponds to a magnetically charged black hole. We also present a singularity-free particlelike solution and a nontrivial black hole solution numerically. Those solutions correspond to the Bartnik-McKinnon solution and a colored black hole with a cosmological constant in four dimensions. We analyze their asymptotic behavior, spacetime structures, and thermodynamical properties. We show that there is a set of stable solutions if the cosmological constant is negative.

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    56
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  • The scalar-tensor theory of gravitation.

    Y.Fujii, K.Maeda

    Cambridge Univ. Press    2003

  • Covariant gravitational equations on brane world with Gauss-Bonnet term

    K.Maeda, T.Torii

    Physical Review   D68, 024002   1 - 14  2003

  • Dynamics of a scalar field in a brane world

    S Mizuno, K Maeda, K Yamamoto

    PHYSICAL REVIEW D   67 ( 2 ) 1 - 15  2003.01  [Refereed]

     View Summary

    We study the dynamics of a scalar field in brane cosmology. We assume that the scalar field is confined in our four-dimensional world. As for the potential of the scalar field, we discuss three typical models: (1) a power-law potential, (2) an inverse-power-law potential, and (3) an exponential potential. We show that the behavior of the scalar field is very different from that in conventional cosmology when the energy density square of the term dominates.

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  • The einstein equations on a brane world.

    K.Maeda

    Progress of Theoretical Physics   Supplement series 148, 59-90 ( 148 ) 59 - 90  2003

     View Summary

    We present effective equations to describe the four-dimensional gravity of a brane world, assuming that a five-dimensional bulk spacetime satisfies the Einstein equations and gravity is confined on the Z_2 symmetric brane. Applying this formalism to the Randall-Sundrum brane world model, we find two new additional terms in the Einstein equations : One is the quadratic term of the energy-momentum tensor of matter field and the other is the 5-dimensional Weyl curvature term. Although the four-dimensional effective equations are not closed and further information from the bulk is required, those terms may provide us windows to search for extra dimensions. We discuss some effects of those terms on cosmology and compact objects. Since those additional terms appear naturally from the present reduction, we apply it to other brane models. We study three models ; the model with a bulk dilaton field motivated by Horava-Witten model, the induced gravity brane model of Dvali, Gabadadze and Porrati, and the R^2 inflationary model proposed by Starobinsky.

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    8
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  • Uniqueness of self-similar asymptotically Friedmann-Robertson-Walker spacetime in Brans-Dicke theory

    H Maeda, J Koga, K Maeda

    PHYSICAL REVIEW D   66 ( 8 ) 1 - 4  2002.10  [Refereed]

     View Summary

    We investigate spherically symmetric self-similar solutions in Brans-Dicke theory. Assuming a perfect fluid with the equation of state p=(gamma-1)mu(1less than or equal togamma&lt;2), we show that there are no nontrivial solutions which approach asymptotically to the flat Friedmann-Robertson-Walker spacetime if the energy density is positive. This result suggests that primordial black holes in Brans-Dicke theory cannot grow at the same rate as the size of the cosmological particle horizon.

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  • Perturbation theory in Lagrangian hydrodynamics for a cosmological fluid with velocity dispersion

    T Tatekawa, M Suda, K Maeda, M Morita, H Anzai

    PHYSICAL REVIEW D   66 ( 6 ) 1 - 13  2002.09  [Refereed]

     View Summary

    We extensively develop a perturbation theory for nonlinear cosmological dynamics, based on the Lagrangian description of hydrodynamics. We solve the hydrodynamic equations for a self-gravitating fluid with pressure, given by a polytropic equation of state, using a perturbation method up to second order. This perturbative approach is an extension of the usual Lagrangian perturbation theory for a pressureless fluid, in view of the inclusion of the pressure effect, which should be taken into account on the occurrence of velocity dispersion. We obtain the first-order solutions in generic background universes and the second-order solutions in a wider range of a polytropic index, whereas our previous work gives the first-order solutions only in the Einstein-de Sitter background and the second-order solutions for the polytropic index 4/3. Using the perturbation solutions, we present illustrative examples of our formulation in one- and two-dimensional systems, and discuss how the evolution of inhomogeneities changes for the variation of the polytropic index.

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    19
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  • Physics of the early universe

    Kei-Ichi Maeda

    Proceedings of the 16th International Conference     425 - 432  2002.09

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  • Conservation laws for collisions of branes and shells in general relativity

    D Langlois, K Maeda, D Wands

    PHYSICAL REVIEW LETTERS   88 ( 18 ) 1 - 4  2002.05  [Refereed]

     View Summary

    We consider the collision of self-gravitating n -branes in a (n + 2) -dimensional spacetime. We show that there is a geometrical constraint which can be expressed as a simple sum rule for angles characterizing Lorentz boosts between branes and the intervening spacetime regions. This constraint can then be reinterpreted as either energy or momentum conservation at the collision.

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    48
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  • Density discontinuity of a neutron star and gravitational waves

    H Sotani, K Tominaga, K Maeda

    PHYSICAL REVIEW D   65 ( 2 )  2002.01  [Refereed]

     View Summary

    We calculate quasinormal f and g modes of a neutron star with density discontinuity, which may appear in a phase transition at an extremely high density. We find that discontinuity will reflect largely on the f mode, and that the g mode could also be important for a less massive star.

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    84
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  • Natural quintessence scenario in a brane world

    S Mizuno, K Maeda

    PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT   148 ( 148 ) 252 - 258  2002  [Refereed]

     View Summary

    We study a new quintessence scenario by a scalar field with an inverse-power potential based on the brane cosmology. We show that in the quadratic dominant stage, which generically appears in brane world cosmology, the density parameter of a scalar field Omega(phi) decreases regardless of the potential-term contribution. This feature enables us to impose natural initial condition. We also discuss the constraints on parameters for the natural and successful quintessence scenario. (1)).

  • Quintessence in a brane world

    S Mizuno, K Maeda

    PHYSICAL REVIEW D   64 ( 12 )  2001.12  [Refereed]

     View Summary

    We reanalyze a new quintessence scenario in a brane world model, assuming that a quintessence scalar field is confined in our three-dimensional brane world. We study three typical quintessence models: (1) an inverse-power-law potential, (2) an exponential potential, and (3) a kinetic-term quintessence (k-essence) model. With an inverse-power-law potential model [V(phi) = mu (alpha +4)phi (-alpha)], we show that in the quadratic dominant stage the density parameter of a scalar field Omega (phi) decreases as a(-4(alpha -2)/(alpha +2)) for 2&lt;&lt;alpha&gt;&lt;6, which is followed by the conventional quintessence scenario. This feature provides us wider initial conditions for successful quintessence. In fact, even if the universe is initially scalar-field dominated, it eventually evolves into a radiation dominated era in the &lt;rho&gt;(2)-dominant stage. Assuming an equipartition condition, we discuss constraints on parameters, with the result that alpha greater than or equal to4 is required. This constraint also restricts the value of the five-dimensional Planck mass, e.g., 4x10(-14)m(4)less than or similar tom(5)less than or similar to 3x10(-13)m(4) for alpha =5. For an exponential potential model V =mu (4) exp(-lambda phi /m(4)), we may not find a natural and successful quintessence scenario as it is, while for a kinetic-term quintessence, we find a tracking solution even in the rho (2)-dominant stage, rather than the Omega (phi)-decreasing solution for an inverse-power-law potential. Then we do find a slight advantage in a brane world. Only the density parameter increases more slowly in the rho (2)-dominant stage, which provides a wider initial condition for successful quintessence.

    DOI

    Scopus

    39
    Citation
    (Scopus)
  • Brane quintessence

    K Maeda

    PHYSICAL REVIEW D   64 ( 12 )  2001.12  [Refereed]

     View Summary

    We propose a new quintessence scenario in brane cosmology, assuming that a quintessence field Q is confined in our three-dimensional brane world. With a potential V(Q)=mu (alpha +4)Q(-alpha) (alpha greater than or equal to2), we find that the density parameter of the scalar field decreases as Omega (Q)similar toa(-4(alpha -2)/(alpha +2)) in the epoch of quadratic energy density dominance, if alpha less than or equal to6. This attractor solution is followed by the usual tracking quintessence scenario after a conventional Friedmann universe is recovered. With an equipartition of initial energy density, we find a natural and successful quintessence model for alpha greater than or similar to4.

    DOI

    Scopus

    39
    Citation
    (Scopus)
  • Internal structure of the Skyrme black hole

    T Tamaki, K Maeda, T Torii

    PHYSICAL REVIEW D   64 ( 8 )  2001.10  [Refereed]

     View Summary

    We consider the internal structure of the Skyrme black hole under a static and spherically symmetric ansatz. We concentrate on solutions with node number 1 and with "winding" number 0, where there exist two solutions for each horizon radius, one solution is stable and the other is unstable against linear perturbation. We find that a generic solution exhibits an oscillating behavior near the singularity, similar to a solution in the Einstein-Yang-Mills (EYM) system, and independent of the stability of the solution. Comparing it with that in the EYM system, this oscillation becomes mild because of the mass term of the Skyrme field. We also find Schwarzschild-like exceptional solutions where no oscillating behavior is seen. Contrary to the EYM system where there is one such solution branch if the node number is fixed, there are two branches corresponding to the stable and unstable ones.

  • Brane preheating

    S Tsujikawa, K Maeda, S Mizuno

    PHYSICAL REVIEW D   63 ( 12 )  2001.06  [Refereed]

     View Summary

    We study brane-world preheating in a massive chaotic inflationary scenario where scalar fields are confined on the three-brane. Assuming that the quadratic contribution in energy densities dominates the Hubble expansion rate during preheating, the amplitude of the inflaton decreases slowly relative to the standard dust-dominated case. This leads to an efficient production of chi particles via the nonperturbative decay of the inflaton even if its coupling is of the order of g = 10(-5). We also discuss massive particle creation heavier than the inflaton, which may play an important role for baryogenesis and leptogenesis scenarios.

  • Gravitational waves from a spinning particle scattered by a relativistic star: Axial mode case

    K Tominaga, M Saijo, K Maeda

    PHYSICAL REVIEW D   63 ( 12 )  2001.06  [Refereed]

     View Summary

    We use a perturbation method to study gravitational waves from a spinning test particle scattered by a relativistic star. The present analysis is restricted to axial modes. By calculating the energy spectrum, the wave forms, and the total energy and angular momentum of gravitational waves, we analyze the dependence of the emitted gravitational waves on particle spin. For a normal neutron star, the energy spectrum has one broad peak whose characteristic frequency corresponds to the angular velocity at the turning point (a periastron). Since the turning point is determined by the orbital parameter, there exists a dependence of the gravitational wave on particle spin. We find that the total energy of l = 2 gravitational waves gets larger as the spin increases in the antiparallel direction to the orbital angular momentum. For an ultracompact star, in addition to such an orbital contribution, we find the quasinormal modes excited by a scattered particle, whose excitation rate to gravitational waves depends on the particle spin. We also discuss the ratio of the total angular momentum to the total energy of gravitational waves and explain its spin dependence.

  • Gravitational waves from a spinning particle scattered by a relativistic star: Axial mode case

    K Tominaga, M Saijo, K Maeda

    PHYSICAL REVIEW D   63 ( 12 )  2001.06  [Refereed]

     View Summary

    We use a perturbation method to study gravitational waves from a spinning test particle scattered by a relativistic star. The present analysis is restricted to axial modes. By calculating the energy spectrum, the wave forms, and the total energy and angular momentum of gravitational waves, we analyze the dependence of the emitted gravitational waves on particle spin. For a normal neutron star, the energy spectrum has one broad peak whose characteristic frequency corresponds to the angular velocity at the turning point (a periastron). Since the turning point is determined by the orbital parameter, there exists a dependence of the gravitational wave on particle spin. We find that the total energy of l = 2 gravitational waves gets larger as the spin increases in the antiparallel direction to the orbital angular momentum. For an ultracompact star, in addition to such an orbital contribution, we find the quasinormal modes excited by a scattered particle, whose excitation rate to gravitational waves depends on the particle spin. We also discuss the ratio of the total angular momentum to the total energy of gravitational waves and explain its spin dependence.

  • Properties of black hole solutions in the SU(3) Einstein-Yang-Mills-dilaton system

    T Tamaki, K Maeda, M Inada

    PHYSICAL REVIEW D   63 ( 8 )  2001.04  [Refereed]

     View Summary

    We consider black hole solutions in the SU(3) Einstein-Yang-Mills-dilaton system under the static and spherically symmetric ansatz. We reveal some properties which were not investigated before. In particular, we find that there appears a shell-like structure in the energy density distribution outside the horizon which can be interpreted as a symptom of the instability of black holes.

  • Primordial fractal density perturbations and structure formation in the universe: One-dimensional collisionless sheet model

    T Tatekawa, K Maeda

    ASTROPHYSICAL JOURNAL   547 ( 2 ) 531 - 544  2001.02  [Refereed]

     View Summary

    The two-point correlation function of galaxy distribution shows that structure in the present universe is scale-free up to a certain scale (at least several tens of Mpc), which suggests that a fractal structure may exist. If small primordial density fluctuations have a fractal structure, the present fractal-like nonlinear structure below the horizon scale could be naturally explained. We analyze the time evolution of fractal density perturbations in an Einstein-de Sitter universe, and study how the perturbation evolves and what kind of nonlinear structure will result. We assume a one-dimensional collisionless sheet model with initial Cantor-type fractal perturbations. The nonlinear structure seems to approach some attractor with a unique fractal dimension, which is independent of the fractal dimensions of initial perturbations. A discrete self-similarity in the phase space is also found when the universal nonlinear fractal structure is reached.

  • The origin of fractal distribution in Self gravitating virialized system and Self-organized criticality

    Y. Sota, O. Iguchi, M. Morikawa, T. Tatekawa, K. Maeda

    Phys. Rev.   E64:056133  2001

  • The Einstein equations on the 3-brane world

    T Shiromizu, K Maeda, M Sasaki

    PHYSICAL REVIEW D   62 ( 2 )  2000.07  [Refereed]

     View Summary

    We carefully investigate the gravitational equations of the brane world, in which all the matter forces except gravity are confined on the 3-brane in a 5-dimensional spacetime with Z(2) symmetry. We derive the effective gravitational equations on the brane, which reduce to the conventional Einstein equations in the low energy limit. From our general argument we conclude that the first Randall-Sundrum-type theory predicts that the brane with a negative tension is an antigravity world and hence should be excluded from the physical point of view. Their second-type theory where the brane has a positive tension provides the correct signature of gravity. In this latter case, if the bulk spacetime is exactly anti-de Sitter spacetime, generically the matter on the brane is required to be spatially homogeneous because of the Bianchi identities. By allowing deviations from anti-de Sitter spacetime in the bulk, the situation will be relaxed and the Bianchi identities give just the relation between the Weyl tensor and the energy momentum tensor. In the present brane world scenario, the effective Einstein equations cease to be valid during an era when the cosmological constant on the brane is not well defined, such as in the case of the matter dominated by the potential energy of the scalar field.

  • Global structure of exact cosmological solutions in the brane world

    S Mukohyama, T Shiromizu, K Maeda

    PHYSICAL REVIEW D   62 ( 2 )  2000.07  [Refereed]

     View Summary

    We find the explicit coordinate transformation which links two exact cosmological solutions of the brane world which have been recently discovered. This means that both solutions are exactly the same as each other. One of the two solutions is described by the motion of a domain wall in the well-known five-dimensional Schwarzshild-AdS spacetime. Hence, we can easily understand the region covered by the coordinate used by another solution.

  • Gravity, stability, and energy conservation on the Randall-Sundrum brane world

    M Sasaki, T Shiromizu, K Maeda

    PHYSICAL REVIEW D   62 ( 2 )  2000.07  [Refereed]

     View Summary

    We carefully investigate the gravitational perturbation of the Randall-Sundrum (RS) single brane-world solution [L. Randell and R. Sundrum, Phys. Rev. Lett. 83, 4690 (1999)], based on a covariant curvature tensor formalism recently developed by us. Using this curvature formalism, it is known that the "electric" part of the five-dimensional Weyl tensor, denoted by E-mu nu, gives the leading order correction to the conventional Einstein equations on the brane. We consider the general solution of the perturbation equations for the five-dimensional Weyl tensor caused by the matter fluctuations on the brane. By analyzing its asymptotic behavior in the direction of the fifth dimension, we find the curvature invariant diverges as we approach the Cauchy horizon. However, in the limit of asymptotic future in the vicinity of the Cauchy horizon, the curvature invariant falls off fast enough to render the divergence harmless to the brane world. We also obtain the asymptotic behavior of E-mu nu on the brane at spatial infinity, assuming that the matter perturbation is localized. We find it falls off sufficiently fast and will not affect the conserved quantities at spatial infinity. This indicates strongly that the usual conservation law, such as the ADM energy conservation, holds on the brane as far as asymptotically flat spacetimes are concerned.

  • Generality of singularity avoidance in superstring theory: Anisotropic case

    H Yajima, K Maeda, H Ohkubo

    PHYSICAL REVIEW D   62 ( 2 )  2000.07  [Refereed]

     View Summary

    In the one-loop string effective action, we study a generality of nonsingular cosmological solutions found in the isotropic and homogeneous case. We discuss Bianchi type-I and -IX spacetimes. We find that nonsingular solutions still exist in the Bianchi type-I model around nonsingular flat Friedmann solutions. On the other hand, we cannot find any nonsingular solutions in the Bianchi type-IX model. The nonexistence of a nonsingular Bianchi type-IX universe may be consistent with the analysis of Kawai, Sakagami, and Soda; i.e., the tensor-mode perturbations against a nonsingular flat Friedmann universe are unstable, because the Bianchi type-IX model is regarded as a closed Friedmann universe with a single gravitational wave. With the stability analysis of Kawai, Sakagami, and Soda, the nonsingular universe found in the isotropic case is unstable, and a singularity avoidance may not work in generic spacetimes.

  • Signature of chaos in gravitational waves from a spinning particle

    S Suzuki, K Maeda

    PHYSICAL REVIEW D   61 ( 2 )  2000.01  [Refereed]

     View Summary

    A spinning test particle around a Schwarzschild black hole shows chaotic behavior if its spin is larger than a critical value. We discuss whether or not some peculiar signature of chaos appears in the gravitational waves emitted from such a system. Calculating the emitted gravitational waves by use of the quadrupole formula, we find that the energy emission rate of gravitational waves for a chaotic orbit is about 10 times larger than that for a circular orbit, but the same enhancement is also obtained by a regular "elliptic" orbit. A chaotic motion does not always enhance the energy emission rate maximally. As for the energy spectra of the gravitational waves, we find some characteristic feature for a chaotic orbit. It may tell us how to find the chaotic behavior of the system. Such peculiar behavior, if it is found, may also provide some additional information to determine the parameters of a system such as a spin.

  • Statistical Mechanics of Self-Gravitating System: Cluster Expansion Method

    O.Iguchi, T.Kurokawa, M.Morikawa, A.Nakamichi, Y.Sota, K.Maeda, T.Tatekawa

    Phys. Lett.   A  2000

  • Preheating with nonminimally coupled scalar fields in higher-curvature inflation models

    S Tsujikawa, K Maeda, T Torii

    PHYSICAL REVIEW D   60 ( 12 )  1999.12  [Refereed]

     View Summary

    In higher-curvature inflation models (R + alpha(n)R(n)), we study a parametric preheating of a scalar field chi coupled nonminimally to a spacetime curvature R(xi R chi(2)). In the case of the R-2-inflation model, efficient preheating becomes possible for rather small values of xi, i.e., \xi\less than or similar to several. Although the maximal fluctuation root[chi(2)](max)approximate to 2x10(17) GeV for xi approximate to -4 is almost the same as the chaotic inflation model with a nonminimally coupled chi held, the growth rate of the fluctuation becomes much larger and efficient preheating is realized. We also investigate preheating for the R-4 model and find that the maximal fluctuation is root[chi(2)](max) approximate to 8 x 10(16) GeV for xi approximate to -35. [S0556-2821(99)05522-8].

  • Gravitating monopole and its black hole solution in Brans-Dicke theory

    T Tamaki, K Maeda, T Torii

    PHYSICAL REVIEW D   60 ( 10 )  1999.11  [Refereed]

     View Summary

    We find a self-gravitating monopole and its black hole solution in Brans-Dicke (BD) theory. We mainly discuss the properties of these solutions in the Einstein frame and compare the solutions with those in general relativity (GR) on the following points. From the held distributions of the generic type of self-gravitating monopole solutions, we find that the Yang-Mills potential and the Higgs field hardly depend on the ED parameter for most of the solution. There is an upper Limit of the vacuum expectation value of the Higgs field to which a solution exists, as in GR. Since the ED scalar field has the effect of lessening an effective gauge charge, the upper limit in ED theory (in the omega=0 case) becomes about 30% larger than in GR. In some parameter ranges, then are two nontrivial solutions with the same mass, one of which can be regarded as the excited state of the other. This is confirmed by the analysis by catastrophe theory, which states that the excited solution is unstable. We also find that the ED scalar field varies more for solutions of smaller horizon radii, which can be understood from the differences of the nontrivial structure outside the horizon. A scalar mass and the thermodynamical properties of new solutions are also examined. Our analysis may give insight into solutions in other theories of gravity; particularly, a theory with a dilaton field may show similar effects because of its coupling to a gauge field. [S0556-2821(99)07220-3].

  • 別冊数理科学「重力理論」 物理学の進化と重力;相対論の新しい潮流;ブラックホール熱力学;宇宙物理とゲージ理論

    前田 恵一

    サイエンス社    1999.10

  • Resonant particle production with nonminimally coupled scalar fields in preheating after inflation

    S Tsujikawa, K Maeda, T Torii

    PHYSICAL REVIEW D   60 ( 6 )  1999.09  [Refereed]

     View Summary

    We investigate the resonant particle production of a scalar field chi coupled nonminimally to a spacetime curvature R (xi R chi(2)) as well as to an inflaton field phi (g(2)phi(2)chi(2)) In the case of g less than or similar to 3 x 10(-4), the xi effect assists g resonance in certain parameter regimes. However, for g greater than or similar to 3 x 10(-4), g resonance is not enhanced by the xi effect because of the xi suppression effect as well as a back reaction effect. If xi approximate to -4, the maximal fluctuation of produced chi particles is root[chi(2)](max) approximate to 2 x 10(17) GeV for g less than or similar to 1 x 10(-5), which is larger than the minimally coupled case with g approximate to 1 x 10(-3). [S0556-2821(99)00618-9].

  • Gravitational waves from a test particle scattered by a neutron star: Axial mode case

    K Tominaga, M Saijo, K Maeda

    PHYSICAL REVIEW D   60 ( 2 )  1999.07  [Refereed]

     View Summary

    Using a metric perturbation method, we study gravitational waves from a test particle scattered by a spherically symmetric relativistic star. We calculate the energy spectrum and the waveform of gravitational waves for axial modes. Since metric perturbations in axial modes do not couple to the matter fluid of the star, emitted waves for a normal neutron star show only one peak in the spectrum, which corresponds to the orbital frequency at the turning point, where the gravitational field is strongest. However, for an ultracompact star (the radius R less than or similar to 3M), another type of resonant periodic peak appears in the spectrum. This is just because of an excitation by a scattered particle of axial quasinormal modes, which were found by Chandrasekhar and Ferrari. This excitation comes from the existence of the potential minimum inside of a star. We also find for an ultracompact star many small periodic peaks at the frequency region beyond the maximum of the potential, which would be due to a resonance of two waves reflected by two potential barriers (Regge-Wheeler type and one at the center of the star). Such resonant peaks appear neither for a normal neutron star nor for a Schwarzschild black hole. Consequently, even if we analyze the energy spectrum of gravitational waves only for axial modes, it would be possible to distinguish between an ultracompact star and a normal neutron star (or a Schwarzschild black hole). [S0556-2821(99)06612-6].

  • Monopole inflation in Brans-Dicke theory

    N Sakai, J Yokoyama, K Maeda

    PHYSICAL REVIEW D   59 ( 10 )  1999.05  [Refereed]

     View Summary

    According to previous work, topological defects expand exponentially without end if the vacuum expectation value of the Higgs field is of the order of the Planck mass. We extend the study of inflating topological defects to Brans-Dicke gravity. With the help of numerical simulations we investigate the dynamics and spacetime structure of a global monopole. Contrary to the case of Einstein gravity, any inflating monopole eventually shrinks and takes a stable configuration. We also discuss cosmological constraints on the model parameters. [S0556-2821(99)05410-7].

  • Gauged monopole-bubble

    Y Kim, SJ Lee, K Maeda, N Sakai

    PHYSICS LETTERS B   452 ( 3-4 ) 214 - 220  1999.04  [Refereed]

     View Summary

    The decay of a metastable false vacuum by bubble nucleation is studied in the high temperature limit of the gauge theory in which an SO(3) gauge symmetry is spontaneously broken to an SO(2). The effects of internal symmetry are so drastic that, in addition to the known Euclidean bounce solution, there exists a new bubble solution involving a 't Hooft-Polyakov monopole at its center the moment it is nucleated. The decay rate and evolution are analyzed. (C) 1999 Published by Elsevier Science B.V, All rights reserved.

  • SL(4, R) generating symmetry in five-dimensional gravity coupled to dilaton and three-form

    CM Chen, DV Gal'tsov, K Maeda, SA Sharakin

    PHYSICS LETTERS B   453 ( 1-2 ) 7 - 16  1999.04  [Refereed]

     View Summary

    We give an explicit formulation of the three-dimensional SL(4,R)/SO(2,2) sigma-model representing the five-dimensional Einstein gravity coupled to the dilaton and the three-form field for spacetimes with two commuting Killing vector fields. New matrix representation is obtained which is similar to one found earlier in the four-dimensional Einstein-Maxwell-Dilaton-Axion (EMDA) theory. The SL(4,R) symmetry joins a variety of 5D solutions of different physical types including strings, 0-branes, KK monopoles etc. interpreting them as duals to the four-dimensional Kerr metric translated along the fifth coordinate. The symmetry transformations are used to construct new rotating strings and composite (0-1)-branes endowed with a NUT parameter. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

  • Stability of a dilatonic black hole with a Gauss-Bonnet term

    T Torii, K Maeda

    PHYSICAL REVIEW D   58 ( 8 )  1998.10  [Refereed]

     View Summary

    We investigate the stability of black hole solutions in an effective theory derived from a superstring model, which includes a dilaton field and the Gauss-Bonnet term. The critical solution, below which mass no static solution exists, divides a family of solutions in the mass-entropy diagram into two. The upper branch approaches the Schwarzschild solution in the large mass limit, while the lower branch ends up with a singular solution which has a naked singularity. In order to investigate the stability of black hole solutions, we adopt two methods. The first one is catastrophe theory, with which we discuss the stability of non-Abelian black holes in general relativity. The present system is classified as a fold catastrophe, which is the simplest case. Following catastrophe theory, if we regard entropy and mass as the potential and the control parameter, respectively, we find the lower branch is more unstable than the upper branch. To confirm this, we study the second method, which is a linear perturbation analysis. We find an unstable mode only for the solutions in the lower branch. Hence, our investigation presents one example that catastrophe theory is also applicable for a generalized theory of gravity. [S0556-2821(98)02118-3].

  • Gravitational waves from a spinning particle plunging into a Kerr black hole

    M Saijo, K Maeda, M Shibata, Y Mino

    PHYSICAL REVIEW D   58 ( 6 )  1998.09  [Refereed]

     View Summary

    Using a black hole (BH) perturbation approach, we numerically study gravitational waves from a spinning particle of mass mu and spin s on the equatorial plane plunging into a Kerr BH of mass M and spin a. When we take into account the particle spin s, (a) the motion of the particle changes due to the coupling effects between s and the orbital angular momentum L-z and between s and a, and also (b) the energy momentum tensor of the linearized Einstein equations changes. We calculate the total radiated energy, linear momentum, angular momentum, the energy spectrum, and waveform of gravitational waves, and we find the following features. (1) There are three spin coupling effects: between L-z and a, between s and L-z, and between s and a when s is considered. Among them, (L-z.a) coupling is the most important effect for the amount of gravitational radiation, and the other two effects are not as remarkable as the first one. However, these effects are still important; for example, the total radiated energy changes by a factor of similar to 2 for the case of a/M = 0.6, L-z/mu M = 1.5 if we change s from 0 to less than or similar to M. (2) For the case when one of the three spins (a, L-z, and s) is vanishing, the amount of gravitational radiation becomes larger (smaller) if spin axes of the other two are parallel (antiparallel). For the case when three spins are nonvanishing, the amount of gravitational radiation becomes maximum if all the axial directions of s, a, and L-z coincide. Thus, our calculations indicate that in a coalescence of two black holes(BHs) whose spins and orbital angular momentum are aligned, gravitational waves are emitted most efficiently. [S0556-2821(98)05216-3].

  • Equivalence of black hole thermodynamics between a generalized theory of gravity and the Einstein theory

    J Koga, K Maeda

    PHYSICAL REVIEW D   58 ( 6 )  1998.09  [Refereed]

     View Summary

    We analyze black hole thermodynamics in a generalized theory of gravity whose Lagrangian is an arbitrary function of the metric, the Ricci tensor, and a scalar field. We can convert the theory into the Einstein frame via a "Legendre" transformation or a conformal transformation. We calculate thermodynamical variables both in the original frame and in the Einstein frame, following the Iyer-Wald definition which satisfies the first law of thermodynamics. We show that all thermodynamical variables defined in the original frame are the same as those in the Einstein frame, if the spacetimes in both frames are asymptotically flat, regular, and possess event horizons with nonzero temperatures. This result may be useful to study whether the second law is still valid in the generalized theory of gravity. [S0556-2821(98)01618-X].

  • Renormalization group approach in Newtonian cosmology

    Y Sota, T Kobayashi, K Maeda, T Kurokawa, M Morikawa, A Nakamichi

    PHYSICAL REVIEW D   58 ( 4 )  1998.08  [Refereed]

     View Summary

    We apply the renormalization group (RG) method to examine the observable scaling properties in Newtonian cosmology. The original scaling properties of the equations of motion in our model are modified for averaged observables on constant time slices. in the RG flow diagram, we find three robust fixed points: Einstein-de Sitter, Milne, and quiescent fixed points. Their stability (or instability) property does not change under the effect of fluctuations. Inspired by the inflationary scenario in the early Universe, we see the Einstein-de Sitter fixed point with small fluctuations as the boundary condition at the horizon scale. Solving the RG equations under this boundary condition toward the smaller scales, we find a generic behavior of observables such that the density parameter Omega decreases, while the Hubble parameter H increases for a smaller averaging volume. The quantitative scaling properties are analyzed by calculating the characteristic exponents around each fixed point. Finally we argue the possible fractal structure of the Universe beyond the horizon scale.

  • Innermost stable circular orbit of a spinning particle in Kerr spacetime

    S Suzuki, K Maeda

    PHYSICAL REVIEW D   58 ( 2 )  1998.07  [Refereed]

     View Summary

    We study the stability of circular orbits of spinning test particles in Kerr spacetime. We find that some of the circular orbits become unstable in the direction perpendicular to the equatorial plane, although the orbits are still stable in the radial direction. For the large spin case [S/mu M less than or similar to O(1)], the innermost stable circular orbit I (ISCO) appears before the minimum of the effective potential in the equatorial plane disappears. This changes the radius of the ISCO and therefore the frequency of the last circular orbit. [S0556-2821(98)04014-4].

  • Two boosted black holes in asymptotically de Sitter space-time: Relation between mass and apparent horizon formation

    T Chiba, K Maeda, K Nakao, T Tsukamoto

    PHYSICAL REVIEW D   57 ( 10 ) 6119 - 6126  1998.05  [Refereed]

     View Summary

    We study the apparent horizon for two boosted black holes in asymptotically de Sitter space-time by solving the initial data on a space with punctures. We show that the apparent horizon enclosing both black holes is not formed if the conserved mass of the system (Abbott-Deser mass) is larger than a critical mass. The black hole with too large an AD mass therefore cannot be formed in asymptotically de Sitter space-time even though each black hole has any inward momentum. We also discuss the dynamical meaning of the AD mass by examining the electric part of the Weyl tensor (the tidal force) for various initial data.

  • Non-Abelian black holes in Brans-Dicke theory

    T Tamaki, K Maeda, T Torii

    PHYSICAL REVIEW D   57 ( 8 ) 4870 - 4884  1998.04  [Refereed]

     View Summary

    We find a black hole solution with a non-Abelian field in Brans-Dicke theory. It is an extension of a non-Abelian black hole in general relativity. We discuss two non-Abelian fields: an "SU(2)" Yang-Mills field with a mass (Proca field) and the SU(2)X SU(2) Skyrme field. In both cases, as in general relativity, there are two branches of solutions, i.e., two black hole solutions with the same horizon radius. The masses of both black holes are always smaller than those in general relativity. A cusp structure in the mass-horizon radius (M-g-r(h)) diagram, which is a typical symptom of stability change in catastrophe theory, does not appear in the Brans-Dicke frame but is found in the Einstein conformal frame. This suggests that catastrophe theory may be simply applied for a stability analysis as it is if we use the variables in the Einstein frame. We also discuss the effects of the Brans-Dicke scalar field on black hole structure.

  • Can we detect scalar gravitational waves ?

    Hisa-aki Shinkai, Motoyuki Saijo, Kei-ichi Maeda

    Relativistic Astrophysics and Cosmology     619 - 621  1998

  • Gravitational waves in Brans-Dicke theory: Analysis by test particles around a Kerr black hole

    M Saijo, H Shinkai, K Maeda

    PHYSICAL REVIEW D   56 ( 2 ) 785 - 797  1997.07  [Refereed]

     View Summary

    Analyzing test particles falling into a Kerr black hole, we study gravitational waves in Brans-Dicke theory of gravity. First we consider a test particle plunging with a constant polar angle into a rotating black hole and calculate the waveform and emitted energy of both scalar and tensor modes of gravitational radiation. We find that the waveform as well as the energy of the scalar gravitational waves weakly depends on the rotation parameter of a black hole a and on the polar angle. Second, using a model of a nonspherical dust shell of test particles falling into a Kerr black hole, we study when the scalar modes dominate. When a black hole is rotating, the tensor modes do not vanish even for a ''spherically symmetric'' shell; instead a slightly oblate shell minimizes their energy but with a nonzero finite value, which depends on the Kerr parameter a. As a result, we find that the scalar modes dominate only for highly spherical collapse, but they never exceed the tensor modes unless the Brans-Dicke parameter omega(BD)less than or similar to 750 for a/M=0.99 or unless omega(BD)less than or similar to 20000 for a/M=0.5, where M is the mass of a black hole. We conclude that the scalar gravitational waves with omega(BD)less than or similar to several thousands do not dominate except for very limited situations (observation from the face-on direction of a test particle falling into a Schwarzschild black hole or highly spherical dust shell collapse into a Kerr black hole). Therefore, observation of polarization is also required when we determine the theory of gravity by the observation of gravitational waves.

    DOI

    Scopus

    19
    Citation
    (Scopus)
  • Chaos in Schwarzschild spacetime: The motion of a spinning particle

    S Suzuki, K Maeda

    PHYSICAL REVIEW D   55 ( 8 ) 4848 - 4859  1997.04  [Refereed]

     View Summary

    We study the motion of a spinning test particle in Schwarzschild spacetime, analyzing the Poincare map and the Lyapunov exponent. We find chaotic behavior for a particle with spin higher than some critical value (e.g., S-cr similar to 0.635 mu M for the total angular momentum J = 4 mu M), where mu and M are the masses of a particle and of a black hole, respectively. The inverse of the Lyapunov exponent in the most chaotic case is about five orbiral periods, which suggests that chaos of a spinning particle may become important in some relativistic astrophysical phenomena. The ''effective potential'' analysis enables us to classify the particle orbits into four types as follows. When the total angular momentum J is large, some orbits are bounded and the ''effective potentials'' are classified into two types: (B1) one saddle point (unstable circular orbit) and one minimal point (stable circular orbit) on the equatorial plane exist for small spin; and (B2) two saddle points bifurcate from the equatorial plane and one minimal point remains on the equatorial plane for large spin. When J is small, no bound orbits exist and the potentials are classified into another two types: (U1) no extremal paint is found for small spin; and (U2) one saddle point appears on the equatorial plane, which is unstable in the direction perpendicular to the equatorial plane, for large spin. The types (B1) and (U1) are the same as those for a spinless particle, but the potentials (B2) and (U2) are new types caused by spin-orbit coupling. The chaotic behavior is found only in the type (B2) potential. The ''heteroclinic orbit,'' which could cause chaos, is also observed in type (B2).

  • Dynamics of quiet universes

    H Mutoh, T Hirai, K Maeda

    PHYSICAL REVIEW D   55 ( 6 ) 3276 - 3287  1997.03  [Refereed]

     View Summary

    We study the stability of a contracting silent universe, which is a spacetime with irrotational dust and vanishing magnetic part of the Weyl tensor, H-ab=0. Two general relativistic backgrounds are analyzed: one is an attractor of silent universes, i.e., a locally Kasner spacetime, and the other is a particular class of inhomogeneous Szekeres solutions. In both cases their stabilities against perturbations with a nonzero magnetic part depend on a contraction configuration; a spindlelike collapse is unstable, while a pancakelike collapse is still stable. We also find that a similar instability exists in spindle collapse for a Newtonian case. We conclude that H-ab=0 is not a generic ansatz even in general relativistic dust collapse.

  • Dilatonic black holes with a Gauss-Bonnet term

    Takashi Torii, Hiroki Yajima, Kei-ichi Maeda

    Physical Review D - Particles, Fields, Gravitation and Cosmology   55 ( 2 ) 739 - 753  1997

     View Summary

    We discuss black holes in an effective theory derived from a superstring model, which includes a dilaton field, a gauge field, and the Gauss-Bonnet term. Assuming U(1) or SU(2) symmetry for the gauge field, we find four types of spherically symmetric solutions, i.e., a neutral, an electrically charged, a magnetically charged, and a “colored” black hole, and discuss their thermodynamical properties and fate via the Hawking evaporation process. For neutral and electrically charged black holes, we find a critical point and a singular end point. Below the mass corresponding to the critical point, no solution exists, while the curvature on the horizon diverges and a naked singularity appears at the singular point. A cusp structure in the mass-entropy diagram is found at the critical point and black holes on the branch between the critical and singular points become unstable. For magnetically charged and “colored” black holes, the solution becomes singular just at the end point with a finite mass. Because the black hole temperature is always finite even at the critical point or the singular point, we may conclude that the evaporation process will not be stopped even at the critical point or the singular point, and the black hole will move to a dynamical evaporation phase or a naked singularity will appear. © 1997 The American Physical Society.

    DOI

    Scopus

    170
    Citation
    (Scopus)
  • Dilatonic black holes with a Gauss-Bonnet term

    T Torii, H Yajima, K Maeda

    PHYSICAL REVIEW D   55 ( 2 ) 739 - 753  1997.01  [Refereed]

     View Summary

    We discuss black holes in an effective theory derived from a superstring model, which includes a dilaton field. a gauge field, and the Gauss-Bonnet term. Assuming U(1) or SU(2) symmetry for the gauge field, we find four types of spherically symmetric solutions, i.e., a neutral, an electrically charged, a magnetically charged, and a ''colored'' black hole, and discuss their thermodynamical properties and fate via the Hawking evaporation process. For neutral and electrically charged black holes, we find a critical point and a singular end point. Below the mass corresponding to the critical point. no solution exists, while the curvature on the horizon diverges and a naked singularity appears at the singular point. A cusp structure in the mass-entropy diagram is found at the critical point and black holes on the branch between the critical and singular points become unstable. For magnetically charged and ''colored'' black holes, the solution becomes singular just at the end point with a finite mass. Because the black hole temperature is always finite even at the critical point or the singular point, we may conclude that the evaporation process will not be stopped even at the critical; point or the singular point, and the black hole will move to a dynamical evaporation phase or a naked singularity will appear.

  • Dynamics of topological defects and inflation (vol 53, pg 655, 1996)

    N Sakai, H Shinkai, T Tachizawa, K Maeda

    PHYSICAL REVIEW D   54 ( 4 ) 2981 - 2981  1996.08  [Refereed]

  • The Stuff of the Universe: Dark Matter, Mankind and Anthropic Cosmology

    前田 恵一

    日本物理学会誌/日本物理学会   51;7  1996.07

  • バーチャル・ブラックホール

    前田 恵一

    パリティ/丸善   11;6  1996.06

  • Chaos in static axisymmetric spacetimes .1. Vacuum case

    Y Sota, S Suzuki, K Maeda

    CLASSICAL AND QUANTUM GRAVITY   13 ( 5 ) 1241 - 1260  1996.05  [Refereed]

     View Summary

    We study the motion of a test particle in static axisymmetric vacuum spacetimes and discuss two criteria for strong chaos to occur: (i) a local instability measured by the Weyl curvature, and (ii) a tangle of a homoclinic orbit, which is closely related to an unstable periodic orbit in general relativity. We analyse several static axisymmetric spacetimes and find that the first criterion is a sufficient condition for chaos, at least qualitatively. Although some test particles which do not satisfy the first criterion show chaotic behaviour in some spacetimes, these can be accounted for by the second criterion.

  • Chaos in static axisymmetric spacetimes .1. Vacuum case

    Y Sota, S Suzuki, K Maeda

    CLASSICAL AND QUANTUM GRAVITY   13 ( 5 ) 1241 - 1260  1996.05  [Refereed]

     View Summary

    We study the motion of a test particle in static axisymmetric vacuum spacetimes and discuss two criteria for strong chaos to occur: (i) a local instability measured by the Weyl curvature, and (ii) a tangle of a homoclinic orbit, which is closely related to an unstable periodic orbit in general relativity. We analyse several static axisymmetric spacetimes and find that the first criterion is a sufficient condition for chaos, at least qualitatively. Although some test particles which do not satisfy the first criterion show chaotic behaviour in some spacetimes, these can be accounted for by the second criterion.

  • 双子のパラドックスのなぞをとく

    前田 恵一

    Newton/教育社   16;5  1996.05

  • Tree-level string cosmology

    R Easther, K Maeda, D Wands

    PHYSICAL REVIEW D   53 ( 8 ) 4247 - 4256  1996.04  [Refereed]

     View Summary

    In this paper we examine the classical evolution of a cosmological model derived from the low-energy tree-level limit of a generic string theory. The action contains the metric, dilaton, central charge and an antisymmetric tensor field. We show that with a homogeneous and isotropic metric, allowing spatial curvature, there is a formal equivalence between this system and a scalar field minimally coupled to Einstein gravity in a spatially flat metric. We refer to this system as the shifted frame and using it we describe the full range of cosmological evolution that this model can exhibit. We show that generic solutions begin (or end) with a singularity. As the system approaches a singularity the dilaton becomes large and loop corrections will become important.

  • Superradiance around Rotating Dilatonic Black Holes

    Kei-ichi Maeda

    Proceedings of the Seventh Marcel Grossmann Meeting/World Scientific    1996

  • Stability of Non-Abelian Black Hole and Catastrophe Theory

    Kei-ichi Maeda

    Proceedings of the Seventh Marcel Grossmann Meeting/World Scientific    1996

  • Solitonic Island in the Bubble

    Kei-ichi Maeda

    Proceedings of 2nd Pacific School forTheoretical Physics    1996

  • Monopole Black Hole and Catastrophe Theory

    Kei-ichi Maeda

    Proceedings of the Sixth Seminar on Quantum Gravity/World Scientific    1996

  • Inflation in a Planar Universe

    Kei-ichi Maeda

    Proceedings of the Seventh Marcel Grossmann Meeting/World Scientific    1996

  • How Does Generalization of Einstein's Theory Enhance the Growth Rate of Cosmological Perturbations?

    Kei-ichi Maeda

    Proceedings of the Seventh Marcel Grossmann Meeting/World Scientific    1996

  • Gravitational Collapse in Szekeres Universes

    Kei-ichi Maeda

    5th Workshop on General Relativity and Gravitation    1996

  • Bubbles with O(3)-symmetric Scalar Fieldin Curved Spacetime

    Kei-ichi Maeda

    Proceedings of the Seventh Marcel Grossmann Meeting/World Scientific    1996

  • A Spinning Test Particle in a Relativistic Space Time

    Kei-ichi Maeda

    5th Workshop on General Relativity and Gravitation    1996

  • Evaporation and fate of dilatonic black holes

    JI Koga, KI Maeda

    PHYSICAL REVIEW D   52 ( 12 ) 7066 - 7079  1995.12  [Refereed]

     View Summary

    We study both spherically symmetric and rotating black holes with dilaton coupling and discuss the evaporation of these black holes via Hawking's quantum radiation and their fates. We find that the dilaton coupling constant alpha drastically affects the emission rates, and therefore the fates of the black holes. When the charge is conserved, the emission rate from the nonrotating hole is drastically changed beyond alpha = 1 (a superstring theory) and diverges in the extreme limit. In the rotating cases we analyze the slowly rotating black hole solution with arbitrary alpha as well as three exact solutions: the Kerr-Newman (alpha = 0), Kaluza-Klein (alpha = root 3), and Sen black hole (alpha = 1 and with axion field). Beyond the same critical value of alpha similar to 1, the emission rate becomes very large near the maximally charged limit, while for alpha &lt; 1 it remains finite. The black hole with alpha &gt; 1 may evolve into a naked singularity due to its large emission rate. We also consider the effects of a discharge process by investigating superadiance for the nonrotating dilatonic black hole.

  • COSMIC COLORED BLACK-HOLES

    T TORII, K MAEDA, T TACHIZAWA

    PHYSICAL REVIEW D   52 ( 8 ) R4272 - R4276  1995.10  [Refereed]

     View Summary

    We present spherically symmetric static solutions (a particlelike solution and a black-hole solution) of the Einstein-Yang-Mills system with a cosmological constant. Although their gravitational structures are locally similar to those of the Bartnik-McKinnon particles or the colored black holes, the asymptotic behavior becomes quite different because of the existence of a cosmological horizon. We also discuss their stability by means of a catastrophe theory as well as a linear perturbation analysis and find the number of unstable modes.

  • EXOTIC BLACK-HOLES

    K MAEDA

    JOURNAL OF THE KOREAN PHYSICAL SOCIETY   28   S468 - S492  1995.09  [Refereed]

     View Summary

    We study exotic black holes, which are new types of black holes obtained from unified theories. The exotic black holes we discussed here are classified into two; one is those with dilaton field, and the other contains non-Abelian ''gauge'' fields. We discuss their thermodynamical properties and evolutions. The farmer shows that the superstring predicts a critical dilaton coupling to U(1) field such that the Hawking radiation changes completely beyond the critical value and it diverges in the extreme limit. As a result, a naked singularity may appear at the end of evaporation process for models with larger coupling than the critical value.
    The second type of exotic black holes give non-trivial black holes, which have the first type of hair. Since some of them are stable, this can be regarded as counterexamples of no hair conjecture. The specific heat will change the sign a few times for some range of parameters. The fate of those black holes are as follows:(1) The unstable black holes will becomes the other stable ones including Schwarzschild black hole. (2) The neutral black holes with the ''effective mass'' of non-Abelian fields have the upper bound of the black hole mass, and when the black hole evolves beyond this critical value, it shifts to more stable Schwarzschild black hole. If the black hole evaporates via the Hawking radiation, the stable particle will remain. (3) For the charged black hole such as monopole black hole, since the Reissner-Nordstrom black hole below some critical. mass becomes unstable and there is no Schwarzschild black hole, the monopole black hole is a unique and stable black hole in some range of parameters. When the black hot gets the mass via accretion, it will become the Reissner-Nordstrom trivial black hole, while when it evaporates via the Hawking radiation, the stable regular monopole will remain.

  • 今度こそわかる相対性理論 Q&amp;A

    前田 恵一

    Newton/教育社   15;10  1995.09

  • 入門 ブラックホール宇宙

    前田 恵一

    Newton/教育社   15;7  1995.06

  • NON-ABELIAN BLACK-HOLES AND CATASTROPHE-THEORY .2. CHARGED TYPE

    T TACHIZAWA, K MAEDA, T TORII

    PHYSICAL REVIEW D   51 ( 8 ) 4054 - 4066  1995.04  [Refereed]

  • 宇宙最大の構造

    前田 恵一

    パリティ/丸善   10;4  1995.04

  • NON-ABELIAN BLACK-HOLES AND CATASTROPHE-THEORY - NEUTRAL TYPE

    T TORII, KI MAEDA, T TACHIZAWA

    PHYSICAL REVIEW D   51 ( 4 ) 1510 - 1524  1995.02  [Refereed]

  • Chaos in General Relativity

    Kei-ichi Maeda

    Proceedings of the International Conference on Dynamical Systems and Chaos/World Scientific   国際会議報告  1995

  • Naturalness of inflation

    K Maeda

    BIRTH OF THE UNIVERSE AND FUNDAMENTAL PHYSICS   455   45 - 52  1995  [Refereed]

  • A 3+1-METHOD FOR FINDING PRINCIPAL NULL DIRECTIONS

    L GUNNARSEN, HA SHINKAI, KI MAEDA

    CLASSICAL AND QUANTUM GRAVITY   12 ( 1 ) 133 - 140  1995.01  [Refereed]

     View Summary

    We present a new method for finding principal null directions (PNDs). Because our method assumes as an input the intrinsic metric and extrinsic curvature of a space-like hypersurface, we expect it will be useful to numerical relativists; We illustrate our method by finding the PNDs of the Kastor-Traschen spacetimes, which contain arbitrarily many Q = M black holes in a de Sitter background.

  • SUPERRADIANCE AROUND ROTATING DILATONIC BLACK-HOLES

    J KOGA, K MAEDA

    PHYSICS LETTERS B   340 ( 1-2 ) 29 - 34  1994.12  [Refereed]

     View Summary

    We consider a superradiance effect around rotating dilatonic black holes. We analyze two cases: one is an exact solution with the coupling constant alpha = root 3, which effective action is reduced from the 5-dimensional Kaluza-Klein theory, and the other is a slowly rotating dilatonic black holes with arbitrary coupling constant. We find that there exists a critical value (alpha similar to 1), which is predicted from a superstring model, and the superradiant emission rate with coupling larger than the critical value becomes much higher than the Kerr-Newman case (alpha = 0) in the maximally charged limit. Consequently, 4-dimensional primordial black holes in higher dimensional unified theories are either rotating but almost neutral or charged but effectively non-rotating.

  • COSMIC HOOP CONJECTURE

    T CHIBA, K MAEDA

    PHYSICAL REVIEW D   50 ( 8 ) 4903 - 4913  1994.10  [Refereed]

     View Summary

    We propose a hoop conjecture in the presence of a positive cosmological constant Lambda: when an apparent horizon forms in a gravitational collapse, the matter must be sufficiently compactified such that the circumference C satisfies the condition C less than or similar to 4 pi M less than or similar to 4 pi M(crit), where M is the Abbott-Deser mass of the collapsed body and M(crit) = 1/3 root Lambda. To confirm our conjecture, we investigate two cases; (1) initial data of a prolate or oblate dust spheroid, and (2) the Kastor-Traschen spacetime which describes a black hole collision with Lambda. We also discuss a relation between the hoop conjecture and an appearance of a naked singularity.

  • JUNCTION CONDITIONS OF FRIEDMANN-ROBERTSON-WALKER SPACE-TIMES

    N SAKAI, K MAEDA

    PHYSICAL REVIEW D   50 ( 8 ) 5425 - 5428  1994.10  [Refereed]

     View Summary

    We complete a classification of junctions of two Friedmann-Robertson-Walker space-times bounded by a spherical thin wall. Our analysis covers superhorizon bubbles and thus complements the previous work of Berezin, Kuzumin, and Tkachev. Contrary to subhorizon bubbles, various topology types for superhorizon bubbles are possible, regardless of the sign of the extrinsic curvature. We also derive a formula for the peculiar velocity of a domain wall for all types of junction.

  • GAUGE-INVARIANT COSMOLOGICAL PERTURBATIONS IN GENERALIZED EINSTEIN THEORIES

    T HIRAI, K MAEDA

    ASTROPHYSICAL JOURNAL   431 ( 1 ) 6 - 19  1994.08  [Refereed]

     View Summary

    Using the covariant approach and conformal transformations, we present a gauge-invariant formalism for cosmological perturbations in generalized Einstein theories (GETs), including the Brans-Dicke theory, theories with a non-minimally coupled scalar field and certain curvature-squared theories. We find an enhancement in the growth rate of density perturbations in the Brans-Dicke theory and discuss attractive features of GETs in the structure formation process.

  • GENERALITY OF INFLATION IN A PLANAR UNIVERSE

    H SHINKAI, K MAEDA

    PHYSICAL REVIEW D   49 ( 12 ) 6367 - 6378  1994.06  [Refereed]

     View Summary

    We study a generality of an inflationary scenario by integrating the Einstein equations numerically in a plane-symmetric spacetime. We consider the inhomogeneous spacetimes due to (i) localized gravitational waves with a positive cosmological constant LAMBDA and (ii) an inhomogeneous inflaton field PHI with a potential 1/2m2PHI2. For case (i), we find that any initial inhomogeneities are smoothed out even if waves collide, so that we conclude that inhomogeneity due to gravitational waves does not prevent the onset of inflation. As for case (ii), if the mean value of the inflaton field is initially as large as the condition in an isotropic and homogeneous inflationary model (i.e., the mean value is larger than several times the Planck mass), the field is soon homogenized and the universe always evolves into de Sitter spacetime. This supports the cosmic no hair conjecture in a planar universe. We also discuss the effects of an additional massless scalar field, which are introduced to set initial data in the usual analysis.

  • DYNAMICAL EVOLUTION OF GRAVITATIONAL WAVES IN THE ASYMPTOTICALLY DE SITTER SPACE-TIME.

    M. Shibata, K. Nakao, T. Nakamura, Kei-ichi Maeda

    Phys.Rev.   D50:708-719  1994

  • GRAVITATIONAL MASS IN ASYMPTOTICALLY DE SITTER SPACE-TIMES.

    Ken-ichi Nakao, Tetsuya Shiromizu, Kei-ichi Maeda

    Class.Quant.Grav.   11:2059-2072  1994  [Refereed]

  • STABILITY OF NON-ABELIAN BLACK-HOLES AND CATASTROPHE-THEORY

    K MAEDA, T TACHIZAWA, T TORII, T MAKI

    PHYSICAL REVIEW LETTERS   72 ( 4 ) 450 - 453  1994.01  [Refereed]

     View Summary

    Two types of self-gravitating particle solutions found in several theories with non-Abelian fields are smoothly connected by a family of nontrivial black holes. There exists a maximum point of the black hole entropy where the stability of solutions changes. This criterion is universal, and the changes in stability follow from a catastrophe-theoretic analysis of the potential function defined by black hole entropy.

  • BUBBLE DYNAMICS AND SPACE-TIME STRUCTURE IN EXTENDED INFLATION

    N SAKAI, K MAEDA

    PHYSICAL REVIEW D   48 ( 12 ) 5570 - 5575  1993.12  [Refereed]

     View Summary

    Developing a thin-wall formalism, we study the evolution of bubbles in extended inflation. We find the following two results. (1) Any true vacuum bubble expands, contrary to the results of Goldwirth and Zaglauer, who claim that bubbles created initially later collapse. We show that their initial conditions for collapsing bubbles are physically inconsistent. (2) Concerning the global space-time structure of the Universe in extended inflation, we show that wormholes are produced as in old inflation, resulting in the multiproduction of universes.

  • BUBBLE DYNAMICS IN GENERALIZED EINSTEIN THEORIES

    N SAKAI, K MAEDA

    PROGRESS OF THEORETICAL PHYSICS   90 ( 5 ) 1001 - 1018  1993.11  [Refereed]

     View Summary

    We present a formalism, encompassing an extension of Israel's thin-wall method, for studying the dynamics of bubbles in generalized Einstein theories. We use this formalism to show that in such theories, no bubble can be homogeneous both inside and out. The evolution equations are designed just in terms of variables in homogeneous outside. Only ordinary differential equations, including the initial constraints, arise from our formalism, which makes it useful for a variety of applications.

  • CAN GRAVITATIONAL-WAVES PREVENT INFLATION

    H SHINKAI, K MAEDA

    PHYSICAL REVIEW D   48 ( 8 ) 3910 - 3913  1993.10  [Refereed]

     View Summary

    To investigate the cosmic no hair conjecture, we analyze numerically one-dimensional plane symmetrical inhomogeneities due to gravitational waves in vacuum spacetimes with a positive cosmological constant. Assuming periodic gravitational pulse waves initially, we study the time evolution of those waves and the nature of their collisions. As measures of inhomogeneity on each hypersurface, we use the three-dimensional Riemann invariant I = (3)R(ijkl) (3)R(ijkl) and the electric and magnetic parts of the Weyl tensor. We find a temporal growth of the curvature in the waves' collision region, but the overall expansion of the universe later overcomes this effect. No singularity appears and the result is a ''no hair'' de Sitter spacetime. The waves we study have amplitudes in the range 0.020LAMBDA less-than-or-equal-to I1/2 less-than-or-equal-to 125.0LAMBDA and widths in the range 0.080l(H) less-than-or-equal-to l less-than-or-equal-to 2.5l(H) where l(H) = (LAMBDA/3)-1/2, the horizon scale of de Sitter spacetime. This supports the cosmic no hair conjecture.

  • BLACK-HOLES WITH NON-ABELIAN HAIR AND THEIR THERMODYNAMICAL PROPERTIES

    T TORII, K MAEDA

    PHYSICAL REVIEW D   48 ( 4 ) 1643 - 1651  1993.08  [Refereed]

     View Summary

    We present some black-hole solutions of the Einstein-Yang-Mills-dilaton system and calculate their Hawking temperatures. We find that if the coupling constant of the dilaton is smaller than some critical value, the thermodynamical behavior of these black holes includes two phase transitions at points determined by the value of the mass parameter. The black holes with masses between those two critical values have a positive specific heat. This is also true for the known colored black-hole solutions. We also reanalyze Skyrme black holes and find that there exist two types of solutions (a stable type and an unstable excited type) and these two types converge to a bifurcation point at some critical horizon radius, beyond which there is no Skyrme black hole. The stable black holes have two possible fates: they can evaporate via the Hawking process, and so evolve into a particlelike (Skyrmion) solution, or they can accrete matter and evolve into the Schwarzschild solution. When a Skyrme black hole evolves into a Schwarzschild black hole, its area changes discontinuously, so that we may regard this evolution as a kind of first-order phase transition. The specific heat of stable Skyrme black holes is always negative, while there are either one or three transition points for unstable Skyrme black holes.

  • EXPANDING SHELL AROUND A VOID AND UNIVERSE MODEL

    N SAKAI, K MAEDA, H SATO

    PROGRESS OF THEORETICAL PHYSICS   89 ( 6 ) 1193 - 1201  1993.06  [Refereed]

     View Summary

    Under the thin-shell approximation, we study the expansion of the shell formed around a single spherical void in the dust universe. We find that the peculiar velocity of the shell is determined mostly by the density parameter OMEGA0. It also depends on the interior dust energy density, but is not so sensitive to a cosmological constant. This feature may open a possibility of determining the universe model from the surface motion of voids.

  • COSMIC NO-HAIR THEOREM IN HOMOGENEOUS SPACETIMES .1. BIANCHI MODELS

    Y KITADA, K MAEDA

    CLASSICAL AND QUANTUM GRAVITY   10 ( 4 ) 703 - 734  1993.04  [Refereed]

     View Summary

    Extending our recent proof of the cosmic no-hair theorem for Bianchi models in power-law inflation, we prove a more general cosmic no-hair theorem for all 0 less-than-or-equal-to lambda &lt; square-root 2, where lambda is the coupling constant of an exponential potential of an inflaton phi, exp(-lambdakappaphi). For any initially expanding Bianchi-type model except type IX, we find that the isotropic inflationary solution is the unique attractor and that anisotropies always enhance inflation. For Bianchi IX, this conclusion is also true, if the initial ratio of the vacuum energy LAMBDA(eff) to the maximum 3-curvature (3) R(max) is larger than 1/[3(1 - lambda2/2)] and its time derivative is initially positive. It turns out that the sufficient condition for inflation in Bianchi type-IX spacetimes with cosmological constant LAMBDA, which is a special case of the theorem (lambda = 0), becomes less restrictive than Wald's one. For type IX, we also show a recollapse theorem.

  • CAN LARGE BLACK-HOLES COLLIDE IN DESITTER SPACE-TIME - AN INFLATIONARY SCENARIO OF AN INHOMOGENEOUS UNIVERSE

    T SHIROMIZU, K NAKAO, H KODAMA, K MAEDA

    PHYSICAL REVIEW D   47 ( 8 ) R3099 - R3102  1993.04  [Refereed]

     View Summary

    We investigate black holes in asymptotically de Sitter space-times. We show that a trapped surface always appears inside the event horizon and the total area of the black holes does not decrease as in asymptotically flat space-times. We find, however, that there is an upper bound on the area of apparent horizons in a wide class of asymptotically de Sitter space-times, in contrast with asymptotically flat space-times. This implies that black holes with a large area cannot collide with each other in asymptotically de Sitter space-time, unless a naked singularity is formed. On the basis of these results we argue that the inflationary scenario works even for initially inhomogeneous universes.

  • APPARENT HORIZONS OF AN N-BLACK-HOLE SYSTEM IN A SPACE-TIME WITH A COSMOLOGICAL CONSTANT

    K NAKAO, K YAMAMOTO, K MAEDA

    PHYSICAL REVIEW D   47 ( 8 ) 3203 - 3213  1993.04  [Refereed]

     View Summary

    We present the analytic solution of N Einstein-Rosen bridges (''N black holes'') in the space-time with a cosmological constant LAMBDA and analyze it for one- and two-bridge systems. We discuss the three kinds of apparent horizons: i.e., the black-hole, white-hole, and cosmological apparent horizons. In the case of two Einstein-Rosen bridges, when the ''total mass'' is larger than a critical value, the black-hole apparent horizon surrounding two Einstein-Rosen bridges is not formed even if the distance is very short. Furthermore, in this case, the cosmological apparent horizon enclosing both bridges does not appear. Hence, it seems that when the ''total mass'' is very large, the Einstein-Rosen bridges cannot collapse into one black hole unless the ''gravitational mass'' is released in some way.

  • NUMERICAL STUDY OF COSMIC NO-HAIR CONJECTURE .2. ANALYSIS OF INITIAL DATA

    K NAKAO, K MAEDA, T NAKAMURA, K OOHARA

    PHYSICAL REVIEW D   47 ( 8 ) 3194 - 3202  1993.04  [Refereed]

     View Summary

    We investigate the initial data for localized gravitational waves in space-time with a cosmological constant LAMBDA. Using a conformal transformation, we find that the Hamiltonian and momentum constraints in the conformal frame turn out to be the same as those for a vacuum space-time without LAMBDA. As initial data, we consider Brill's waves in the conformal frame and discuss the trapped and antitrapped surfaces in the physical frame. Just as Brill's wave in asymptotically flat space-time, the gravitational ''mass'' of our case is positive; however, the waves with a large gravitational mass do not always provide trapped surfaces in contrast with the case of LAMBDA = 0. The large amount of gravitational waves, hence, does not seem to be an obstacle to the cosmic no-hair conjecture.

  • SUPERRADIANCE IN THE KERR-DESITTER SPACE-TIME

    T TACHIZAWA, K MAEDA

    PHYSICS LETTERS A   172 ( 5 ) 325 - 330  1993.01  [Refereed]

     View Summary

    A Kerr-de Sitter black hole loses energy and angular momentum through both quantum superradiance and thermal emission. Our investigation of the former process indicates that a rapidly rotating black hole spins down faster as we increase LAMBDA, but after spinning down takes longer to evaporate.

  • BUBBLE DYNAMICS IN GENERALIZED EINSTEIN THEORIES.

    Nobuyuki Sakai, Kei-ichi Maeda

    Prog.Theor.Phys.   90:1001-1018  1993

  • COSMIC NO-HAIR THEOREM IN POWER-LAW INFLATION

    Y KITADA, K MAEDA

    PHYSICAL REVIEW D   45 ( 4 ) 1416 - 1419  1992.02  [Refereed]

     View Summary

    We prove a cosmic no-hair theorem for Bianchi models in power-law inflation. Provided that the potential of an inflation phi is exp( -lambda-kappa-phi) with 0 less-than-or-equal-to lambda &lt; square-root 2/3, we find that the isotropic power-law solution is the unique attractor for any initially expanding Bianchi-type models except type IX. For Bianchi type IX, this conclusion is also true if the initial ratio of the vacuum energy to the maximum three-curvature is larger than one half.

  • INFLATION IN GENERALIZED EINSTEIN THEORIES

    AL BERKIN, K MAEDA

    PHYSICAL REVIEW D   44 ( 6 ) 1691 - 1704  1991.09  [Refereed]

     View Summary

    We analyze the details of soft inflationary models, which have two scalar fields: one is the standard inflaton, whose potential is exponentially coupled to the other field. Such models are derived from both fundamental theories, and in the conformal frame of generalized Einstein theories. In the latter case, a nonstandard exponential coupling to the inflaton kinetic term also may arise. We list and discuss the various theories which give soft inflation, and then consider the satisfaction of the inflationary constraints in general models. We then specialize to new and chaotic inflation potentials, with both standard and nonstandard kinetic terms. The density perturbations are reduced sufficiently so that new inflation works well, with the coupling constant near the values allowed by grand unified theories. For chaotic inflation with a massive inflaton, we find successful inflation without any fine-tuning of the coupling constant or initial data.

  • NUMERICAL STUDY OF COSMIC NO-HAIR CONJECTURE - FORMALISM AND LINEAR-ANALYSIS

    K NAKAO, T NAKAMURA, K OOHARA, K MAEDA

    PHYSICAL REVIEW D   43 ( 6 ) 1788 - 1797  1991.03  [Refereed]

     View Summary

    Three-dimensional numerical relativity is applied to an investigation of the so-called "cosmic no-hair conjecture," which has been proposed to explain the homogeneity and isotropy of the present Universe via the inflationary scenario. We present a general formalism to study this cosmological problem using numerical relativity. Following this formalism, we find general solutions of the linearized Einstein equation in the de Sitter background and discuss a homogenization mechanism in the linear regime.

  • THE CONSTANT-MEAN-CURVATURE SLICING OF THE SCHWARZSCHILD-DE SITTER SPACE-TIME

    K NAKAO

    PRIMORDIAL NUCLEOSYNTHESIS AND EVOLUTION OF EARLY UNIVERSE   169   277 - 278  1991  [Refereed]

  • EXTENDED INFLATIONARY UNIVERSES

    JD BARROW, K MAEDA

    NUCLEAR PHYSICS B   341 ( 1 ) 294 - 308  1990.09  [Refereed]

  • EFFECTS OF R3 AND R-CLASS-R TERMS ON R2-INFLATION

    AL BERKIN, K MAEDA

    PHYSICS LETTERS B   245 ( 3-4 ) 348 - 354  1990.08  [Refereed]

  • SOFT INFLATION

    AL BERKIN, K MAEDA, J YOKOYAMA

    PHYSICAL REVIEW LETTERS   65 ( 2 ) 141 - 144  1990.07  [Refereed]

  • WORMHOLES WITH SCALAR FIELDS

    DH COULE, K MAEDA

    CLASSICAL AND QUANTUM GRAVITY   7 ( 6 ) 955 - 963  1990.06  [Refereed]

  • QUANTUM COSMOLOGICAL APPROACH TO THE COSMIC NO-HAIR CONJECTURE IN THE BIANCHI TYPE-IX SPACETIME

    J YOKOYAMA, K MAEDA

    PHYSICAL REVIEW D   41 ( 4 ) 1047 - 1053  1990.02  [Refereed]

  • INFLATION IN A RENORMALIZABLE COSMOLOGICAL MODEL AND THE COSMIC NO-HAIR CONJECTURE

    K MAEDA, JA STEINSCHABES, T FUTAMASE

    PHYSICAL REVIEW D   39 ( 10 ) 2848 - 2853  1989.05  [Refereed]

  • TOWARDS THE EINSTEIN-HILBERT ACTION VIA CONFORMAL-TRANSFORMATION

    K MAEDA

    PHYSICAL REVIEW D   39 ( 10 ) 3159 - 3162  1989.05  [Refereed]

  • CHAOTIC INFLATIONARY SCENARIO IN MODELS HAVING NONMINIMAL COUPLING WITH CURVATURE.

    T. Futamase, Kei-ichi Maeda

    Phys.Rev.   D39:399-404  1989

  • BARYON NUMBER GENERATION FROM COSMIC STRING LOOPS

    M KAWASAKI, K MAEDA

    PHYSICS LETTERS B   208 ( 1 ) 84 - 88  1988.07  [Refereed]

  • FINITE-WIDTH CORRECTIONS TO THE NAMBU ACTION FOR THE NIELSEN-OLESEN STRING

    K MAEDA, N TUROK

    PHYSICS LETTERS B   202 ( 3 ) 376 - 380  1988.03  [Refereed]

  • BLACK-HOLES AND MEMBRANES IN HIGHER-DIMENSIONAL THEORIES WITH DILATON FIELDS

    GW GIBBONS, K MAEDA

    NUCLEAR PHYSICS B   298 ( 4 ) 741 - 775  1988.03  [Refereed]

  • ON TIME-VARIATION OF FUNDAMENTAL CONSTANTS IN SUPERSTRING THEORIES

    K MAEDA

    MODERN PHYSICS LETTERS A   3 ( 3 ) 243 - 249  1988.02  [Refereed]

  • INFLATION AS A TRANSIENT ATTRACTOR IN R2 COSMOLOGY

    K MAEDA

    PHYSICAL REVIEW D   37 ( 4 ) 858 - 862  1988.02  [Refereed]

  • IS THE COMPACTIFIED VACUUM SEMICLASSICALLY UNSTABLE

    K MAEDA

    PHYSICS LETTERS B   186 ( 1 ) 33 - 37  1987.02  [Refereed]

  • ATTRACTOR IN A SUPERSTRING MODEL - THE EINSTEIN THEORY, THE FRIEDMANN UNIVERSE, AND INFLATION

    K MAEDA

    PHYSICAL REVIEW D   35 ( 2 ) 471 - 479  1987.01  [Refereed]

    DOI

    Scopus

    17
    Citation
    (Scopus)
  • INITIAL CONDITIONS AND ATTRACTORS IN HIGHER-DIMENSIONAL COSMOLOGIES

    K MAEDA, PYT PANG

    PHYSICS LETTERS B   180 ( 1-2 ) 29 - 33  1986.11  [Refereed]

  • INFLATION IN A SUPERSTRING MODEL

    K MAEDA, MD POLLOCK, CE VAYONAKIS

    CLASSICAL AND QUANTUM GRAVITY   3 ( 5 ) L89 - L97  1986.09  [Refereed]

  • BUBBLE DYNAMICS IN THE EXPANDING UNIVERSE

    K MAEDA

    GENERAL RELATIVITY AND GRAVITATION   18 ( 9 ) 931 - 951  1986.09  [Refereed]

  • ON INFLATION IN THE HETEROTIC SUPERSTRING MODEL

    K MAEDA, MD POLLOCK

    PHYSICS LETTERS B   173 ( 3 ) 251 - 256  1986.06  [Refereed]

  • STABILITY AND ATTRACTOR IN A HIGHER-DIMENSIONAL COSMOLOGY .1.

    K MAEDA

    CLASSICAL AND QUANTUM GRAVITY   3 ( 2 ) 233 - 247  1986.03  [Refereed]

  • STABILITY AND ATTRACTOR IN KALUZA-KLEIN COSMOLOGY. 1.

    Kei-ichi Maeda

    Class. Quant.   Grav.3:233  1986

  • COSMOLOGICAL SOLUTIONS WITH CALABI-YAU COMPACTIFICATION

    K MAEDA

    PHYSICS LETTERS B   166 ( 1 ) 59 - 64  1986.01  [Refereed]

  • ATTRACTOR UNIVERSE IN SIX-DIMENSIONAL N=2 SUPERGRAVITY KALUZA-KLEIN THEORY.

    Kei-ichi Maeda, H. Nishino

    Phys. Lett.   B158:381  1985

  • QUANTUM EFFECTS ON HIGHER DIMENSIONAL SPACE-TIME

    U CAROW, K MAEDA

    PHYSICS LETTERS B   158 ( 4 ) 298 - 304  1985  [Refereed]

  • AN ATTRACTOR UNIVERSE IN 6-DIMENSIONAL N = 2 SUPERGRAVITY KALUZA-KLEIN THEORY

    K MAEDA, H NISHINO

    PHYSICS LETTERS B   158 ( 5 ) 381 - 387  1985  [Refereed]

  • COSMOLOGICAL SOLUTIONS IN D=6, N=2 KALUZA-KLEIN SUPERGRAVITY - THE FRIEDMANN UNIVERSE WITHOUT FINE-TUNING

    K MAEDA, H NISHINO

    PHYSICS LETTERS B   154 ( 5-6 ) 358 - 362  1985  [Refereed]

  • QUANTUM EFFECT ON KALUZA-KLEIN COSMOLOGIES - HIGH-TEMPERATURE CASE

    K MAEDA

    PHYSICAL REVIEW D   32 ( 10 ) 2528 - 2538  1985  [Refereed]

  • Particle creation effect on M4×S7 Kaluza-Klein cosmologies

    Takao Koikawa, Kei-ichi Maeda

    Physics Letters B   149 ( 1-3 ) 82 - 86  1984.12

     View Summary

    The particle creation effect on the higher-dimensional Kaluza-Klein cosmologies with M4×S7 topology is studied. This quantum effect is found to change the classical behavior of the internal and external scale factors drastically in the early stage of the expansion, so that the dimensional reduction seems to fail. However, at the later stage two scale factors get separated from each other and the internal scale factor approaches the final singularity just like the vacuum case. © 1984.

    DOI

    Scopus

    11
    Citation
    (Scopus)
  • EFFECT OF PARTICLE CREATION ON KALUZA-KLEIN COSMOLOGIES.

    Kei-ichi Maeda

    Phys. Rev.   D30:2482-2494  1984

  • PARTICLE CREATION EFFECT ON M4XS7 KALUZA-KLEIN COSMOLOGIES

    T KOIKAWA, K MAEDA

    PHYSICS LETTERS B   149 ( 1-3 ) 82 - 86  1984  [Refereed]

  • IS COSMOLOGICAL DIMENSIONAL REDUCTION POSSIBLE

    K MAEDA

    PHYSICS LETTERS B   138 ( 4 ) 269 - 273  1984  [Refereed]

  • PARTICLE CREATION EFFECT ON M4XS7 KALUZA-KLEIN COSMOLOGIES

    T KOIKAWA, K MAEDA

    PHYSICS LETTERS B   149 ( 1-3 ) 82 - 86  1984  [Refereed]

  • VOID IN THE CLOSED UNIVERSE

    K MAEDA, M SASAKI, H SATO

    PROGRESS OF THEORETICAL PHYSICS   69 ( 1 ) 89 - 99  1983  [Refereed]

  • EXPANSION OF A THIN SHELL AROUND A VOID IN EXPANDING UNIVERSE

    K MAEDA, H SATO

    PROGRESS OF THEORETICAL PHYSICS   70 ( 3 ) 772 - 782  1983  [Refereed]

  • THE EXPANSION LAW OF THE VOID IN THE EXPANDING UNIVERSE

    H SATO, K MAEDA

    PROGRESS OF THEORETICAL PHYSICS   70 ( 1 ) 119 - 127  1983  [Refereed]

  • EXPANSION OF A THIN SHELL AROUND A VOID IN EXPANDING UNIVERSE

    K MAEDA, H SATO

    PROGRESS OF THEORETICAL PHYSICS   70 ( 3 ) 772 - 782  1983  [Refereed]

  • GENERAL RELATIVISTIC GRAVITATIONAL COLLAPSE OF ROTATING STAR WITH MAGNETIC-FIELDS - THE FORMALISM AND THE INITIAL-VALUE EQUATIONS

    K MAEDA, K OOHARA

    PROGRESS OF THEORETICAL PHYSICS   68 ( 2 ) 567 - 579  1982  [Refereed]

  • CREATION OF SCHWARZSCHILD DE SITTER WORMHOLES BY A COSMOLOGICAL 1ST-ORDER PHASE-TRANSITION

    KI MAEDA, K SATO, M SASAKI, H KODAMA

    PHYSICS LETTERS B   108 ( 2 ) 98 - 102  1982  [Refereed]

  • MULTI-PRODUCTION OF UNIVERSES BY 1ST-ORDER PHASE-TRANSITION OF A VACUUM

    K SATO, H KODAMA, M SASAKI, KI MAEDA

    PHYSICS LETTERS B   108 ( 2 ) 103 - 107  1982  [Refereed]

  • Topology of Collapse in Conformal Diagrams &#8211; Reissner -Nordstom case&#8211;

    F. de Felice, K. Maeda

    Prog. Theor. Phys.   68: 1967-1978  1982

  • CREATION OF WORMHOLES BY 1ST ORDER PHASE-TRANSITION OF A VACUUM IN THE EARLY UNIVERSE

    K SATO, M SASAKI, H KODAMA, K MAEDA

    PROGRESS OF THEORETICAL PHYSICS   65 ( 4 ) 1443 - 1446  1981  [Refereed]

  • FATE OF WORMHOLES CREATED BY 1ST-ORDER PHASE-TRANSITION IN THE EARLY UNIVERSE

    H KODAMA, M SASAKI, K SATO, K MAEDA

    PROGRESS OF THEORETICAL PHYSICS   66 ( 6 ) 2052 - 2072  1981  [Refereed]

  • General Relativistic Collapse of an Axially Symmetric Star I - The Formalism and the Initial Value Equations -

    T. Nakamura, K. Maeda, S. Miyama, M. Sasaki

    Prog. Theor. Phys.   63:1229  1980

  • A METHOD OF DETERMINING APPARENT HORIZONS IN [(2+1)+1]-FORMALISM OF THE EINSTEIN EQUATIONS

    M SASAKI, K MAEDA, S MIYAMA, T NAKAMURA

    PROGRESS OF THEORETICAL PHYSICS   63 ( 3 ) 1051 - 1053  1980  [Refereed]

  • GRAVITATIONAL COLLAPSE OF CHARGED DUST SHELL AND MAXIMAL SLICING CONDITION

    K MAEDA

    PROGRESS OF THEORETICAL PHYSICS   63 ( 2 ) 425 - 437  1980  [Refereed]

  • AN ANALYTIC SOLUTION OF INITIAL DATA FOR SLOWLY ROTATING DUST SPHERE UNDER MAXIMAL SLICING CONDITION

    K MAEDA, S MIYAMA, M SASAKI, T NAKAMURA

    PROGRESS OF THEORETICAL PHYSICS   63 ( 3 ) 1048 - 1050  1980  [Refereed]

  • NEW FORMALISM OF THE EINSTEIN EQUATIONS FOR RELATIVISTIC ROTATING SYSTEMS

    KI MAEDA, M SASAKI, T NAKAMURA, S MIYAMA

    PROGRESS OF THEORETICAL PHYSICS   63 ( 2 ) 719 - 721  1980  [Refereed]

  • INSTABILITY OF A QUANTUM FIELD IN THE CURVED SPACE-TIME OF A ROTATING STAR.

    H. Sato, Kei-ichi Maeda

    Prog.Theor.Phys.   59:1173-1187  1978

  • NO SUPERRADIANCE OF SPINOR WAVE IN THE KERR-NEWMAN METRIC.

    Kei-ichi Maeda

    Prog.Theor.Phys.   55   1677 - 1678  1976

  • 数理科学「量子論と相対論」

    前田 恵一

    サイエンス社  

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Books and Other Publications

  • 演習形式で学ぶ特殊相対性理論

    前田, 恵一, 田辺, 誠( Part: Joint author)

    サイエンス社  2022.04 ISBN: 9784781915418

  • 天体物理学の基礎 II

    牧野淳一郎, 前田恵一, 田中貴浩, 星野真弘, 服部誠( Part: Contributor)

    日本評論社  2008.05 ISBN: 9784535607316

  • 重力理論講義 ー 相対性理論と時空物理学の進展

    前田恵一( Part: Sole author)

    2008.05

  • 複雑さと法則 (複雑系叢書5)

    早稲田大学複雑系高等学術研究所編, 永井善則, 相沢洋二, 原山卓久, 山中由也, 森川雅博, 前田恵一( Part: Contributor)

    共立出版  2006.11 ISBN: 432003449X

    ASIN

  • The scalar-tensor theory of gravitation

    Yasunori Fujii, Kei-ichi Maeda( Part: Joint author)

    Cambridge University Press  2003.03 ISBN: 0521037522

    ASIN

  • 図解雑学 ブラックホール

    前田, 恵一( Part: Supervisor (editorial))

    ナツメ社  2000.12 ISBN: 4816328068

    ASIN

  • アインシュタインとボーア: 相対論・量子論のフロンティア

    日本物理学会, 前田, 恵一, 江沢, 洋, 高木, 伸, 上田, 正仁, 霜田, 光一, 二宮, 正夫, 荒船, 次郎, 川合, 光, 池内, 了, 佐藤, 勝彦, 井元, 信之( Part: Contributor)

    裳華房  1999.10 ISBN: 4785328142

    ASIN

  • 図解雑学 ビッグバン

    前田, 恵一( Part: Supervisor (editorial))

    ナツメ社  1999.09 ISBN: 4816326499

    ASIN

  • アインシュタインの時間―解き明かされる相対性理論のパラドックス

    前田 恵一( Part: Sole author)

    ニュートンプレス  1998.11 ISBN: 4315515191

    ASIN

  • カオスとの遭遇―力学系への数学的アプローチ

    前田 恵一, 原山卓久( Part: Joint translator)

    産業図書  1995.05 ISBN: 4782810091

    ASIN

  • 宇宙の謎が解ける本―大人も子どもも楽しめるサイエンス

    インターシップ( Part: Supervisor (editorial))

    ジャパンミックス  1995.05 ISBN: 4883213684

    ASIN

  • 宇宙のトポロジー (NEW SCIENCE AGE)

    前田 恵一( Part: Sole author)

    岩波書店  1991.12 ISBN: 4000074075

    ASIN

▼display all

Misc

Research Projects

  • 様々な相対論的重力現象解析に基づく重力の本質理解に向けて

    Project Year :

    2019.04
    -
    2022.03
     

     View Summary

    重力を時空の幾何学として捉える一般相対論は宇宙論、ブラックホール、重力波というまったく新しい研究分野を開拓した。本研究では三体重力系のような非可積分系のダイナミクス、特にそのような系から放出される重力波の解析により、重力の新しい側面を明らかにする。一方、超ミクロの世界と超マクロの世界の両極端で人類は大きな謎に遭遇しているが、本研究では一般相対論を超える理論や考え方によってこれらの謎解明に迫る。重力を時空の幾何学として捉える一般相対論は宇宙論、ブラックホール、重力波というまったく新しい研究分野を開拓した。本研究では三体重力系のような非可積分系のダイナミクス、特にそのような系から放出される重力波の解析により、重力の新しい側面を明らかにすることを目的とし、本年度は特に階層三体重力系(近接連星が第3の天体と連星系を構成する三体系)に特徴的な古在・リドフ振動の詳細な解析を行い、そのような系から放出される重力波の観測可能性について考察した。その結果、重力波の間接的証拠となるパルサーの近星点移動曲線の屈折が観測的にみられることを予言し、また直接観測に関しては、内部連星が合体する以前においてもLISAなどの次世代観測機器により十分に観測可能であることを示した。一方、超ミクロの世界と超マクロの世界の両極端で人類は大きな謎に遭遇しているが、本研究では一般相対性理論を超える理論や考え方によってこれらの謎解明に迫る。まずは従来の研究の延長上として、これらの謎解明に向けた修正重力理論に基づく様々な重力現象の解析を行っているが、重力波伝播速度が光速度とほぼ同じである制限はこのアプローチに大きな制限を与えている。そこで本研究で遂行する新しいアプローチ開拓の第一歩としてAdS/CFT対応を基礎にした重力理論構築に向けた準備研究をスタートした。特にCFT側から適切な境界条件を課すことで、ディープラーニングなどの手法を用いて重力側においてどのような重力理論が発現するかを探索中である。第一の課題に対して2019年度は、主に階層的三体系からの重力波観測の可能性について調べた。階層的三体系に特徴的な古在・リドフ振動により内連星の離心率が変化し、重力波放出量も変化することで、パルサーの近星点移動曲線の屈折が観測的にみられることを予言し、その成果をMonthly Notices Letters に掲載した。さらに相対論的効果を考慮した階層的三体系から放出される重力波の波形やスペクトルの詳細な解析を行い、予想される重力波が将来の観測計画(LISA、DECIGO、BBO)において十分に観測可能であることを明らかにした。この系からの重力波は、一度発見すればその後は古在・リドフ振動周期で何度も観測可能になるため、次の観測に向けた準備期間が十分得られることからより詳細な解析を可能にする(Phys.Rev.D に掲載)。第二の課題に対しては、いくつかの修正重力理論(Metric-affine Gravity、DBI-Galileon gravity、hybrid Higgs inflation model)に基づき、宇宙初期の加速膨張(インフレーション)および現在の加速膨張(ダークエネルギー)のメカニズムについて解析を行った。また、ローレンツ不変性を破る理論に基づきkink・anti-kink の衝突現象を解析し、フラクタルなどの非線形物理学にみられる特徴的な振る舞いを明らかにしている。AdS/CFT対応を基礎にしたアプローチに関しては、研究をスタートした段階でまだほとんど結果は得られていないが、研究の方向性は明確になってきており、短い期間で興味深い結果が得られるものと期待している。新型コロナ感染症の問題により、これまで考えていた研究の方法は大きく変える必要が出てきた。当初の予定では、共同研究を行う学生が少なくなってきたこともあり、海外の第一線で活躍する研究者との共同研究を中心にした研究を行うことを考えていた。しかしながら現在はそのような研究はかなり難しくなり、新しい研究方法が必要となった。第一の課題に関しては早稲田大学の研究員や学生および京大の学生との共同研究で、スカイプを使った共同研究を行っており、今後もその方法により予定している研究が遂行可能と考えられる。今後は予定通り、高次のポストニュートン近似項を考慮した場合の階層的三体系およびその系からの重力波解析、輻射の反作用を考慮した階層的三体系からの重力波解析、最終的には数値相対論に基づくより一般的な三体系からの重力波解析を行う。第二の課題に関しても、同じようなネットワークを構成することで、当初の研究内容を遂行することを考えている。実際、テーマは少し異なるか、先日早稲田大学高等研究所に滞在していた研究者と共同研究を始めたが、現在はZoomを使った議論およびメールにより研究を遂行している。第二の課題に関しても同様の方法を用いて行うことを現在検討中である

  • New developments of gravity theory research in gravitational wave physics / astronomy

    Project Year :

    2017.06
    -
    2022.03
     

  • 重力波物理学・天文学における重力理論研究の新展開

    科学研究費助成事業(京都大学)・基礎物理学研究所  新学術領域(研究領域提案型)

    Project Year :

    2017
    -
    2021
     

  • Systematic Study with Organized Combinations of Three Approaches for Gravitational Theories

    Project Year :

    2016.04
    -
    2019.03
     

     View Summary

    General Relativity has been confirmed by many experiments and observations. However, we have also found very important and serious mysteries in cosmology and gravitation (dark energy and inflation). In order to solve those problems, many modified gravitational theories have been proposed. To judge which theory is correct, we believe that we should perform a systematic study of those theories instead of independent analysis. Here I have proposed three approaches for gravitational theories ([I] Effective Field Approach, [II] Fundamental Theoretical Approach, [III] General Relativistic Approach), and performed a systematic study with organized combinations of those three approaches to analyze dark energy problem and inflation

  • 3つの系統的アプローチの有機的な組み合わせによる様々な重力理論の検証

    科学研究費助成事業(早稲田大学) 

    Project Year :

    2016.04
    -
    2019.03
     

  • Comprehensive Research of Core-Collapse Supernovae and The Evolution of Massive Stars

    Project Year :

    2012.04
    -
    2016.03
     

     View Summary

    In this project, we have conducted theoretical investigations on the evolution of massive stars from the quasi-static phase through the gravitational core-collapse and the subsequent supernova explosion up to the formation of a neutron star or a black hole. We have first performed approximate simulations of core-collapse and explosion for several hundreds of models and made clear that the compactness of the stellar core just prior to the collapse is the single most important quantity to determine the success or failure of explosion. We have also accomplished more rigorous simulations on the K supercomputer and demonstrated that the most sophisticated computations cannot reproduce the supernova explosion. We have then upgraded our code so that general relativity could be handled. We have finally developed a novel formulation to numerically obtain various stellar configurations in rotational equilibrium so that we could study the effect of rotation on the evolution of massive stars

  • 素粒子統一理論を基礎にした様々な重力理論の解析および宇宙論的検証

    科学研究費助成事業(早稲田大学)  科学研究費助成事業(基盤研究(C))

    Project Year :

    2013.04
    -
    2016.03
     

     View Summary

    宇宙論の標準モデルであるビッグバン宇宙論は、近年の精密観測により確かなものになってきたが、その一方で新たな謎としてダークエネルギー問題が誕生した。その解決には自然界における基本法則の根幹にも関わる発想の転換が必要と考えられる。また、ミクロ世界においてはインフレーション宇宙論などの初期宇宙像の観測的検証が注目されており、素粒子統一理論をもとにしたその基本的理解が求められている。これらミクロとマクロの両極端で謎となっている加速膨張宇宙の起源の解明には宇宙を支配する重力の本質的理解が鍵となり、一般相対性理論を超えた様々な重力理論が提案されるに至っている。本研究では、超弦理論など素粒子統一理論の立場からダークエネルギー・インフレーションなどの宇宙の未解決重要課題を重力物理学の問題として系統的に解析する。
    2013年度は主に以下の研究成果を得ている。
    (I)素粒子統一理論を基礎にした様々な重力理論に基づくインフレーションの解析を行っているが、近年ゲージ場とインフラトン場の結合の重要性が指摘されており、2013年度は、特に、ゲージ場のインフレーションモデルに与える影響を解析した。複数のU(1) ゲージ場またはSU(2) ゲージ場がインフラトン場と結合する場合、一様等方加速膨張時空が安定解として存在するが、初期の非等方性が大きい場合は、長期間非等方加速膨張が起こり、モデルが観測的に検証可能であることを示した。
    (II)ダークエネルギー問題に関しては、2013年度は、massive gravity 理論を拡張したbigravity理論を基礎に解析した。その結果、加速膨張宇宙がアトラクターとして動的に実現されるということ、さらには第二の計量と結合する「双子物質」が我々の宇宙のダークマターとして振る舞う可能性があることを示した。

  • Analysis and cosmological verification of various gravitational theories based on unified theory of fundamental interactions

    Project Year :

    2013.04
    -
    2016.03
     

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    We analyse various gravity theories which may resolve two most important subjects in modern cosmology (inflation and dark energy problem) based on the unified theory of fundamental interactions. We propose two new inflationary scenarios (Higgs inflation based on standard model of particle physics and KKLMMT inflation based on superstring theory), which are extended from the original models and satisfy the observational constraints well. As for the dark energy problem, we mainly analyse bigravity theory, in which one of gravitons is massive. We show that it may resolves the dark matter problem as well as the dark energy problem

  • Research on Gravitational Physics based in a Cosmological Setting

    Project Year :

    2010.04
    -
    2013.03
     

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    We study most fundamental and important subjects on cosmology as gravitational physics. As for the subject on the early universe, we analyze the so called cosmological singularity problem by Horava-Lifshitz gravity theory and the origin of inflation based on superstring theory. We also study dark energy problem mainly by a bigravity theory. We find that dark energy (a cosmological constant) naturally appears as an attractor in this model

  • 高次元宇宙における重力理論と宇宙論

    二国間交流事業(日本・イギリス(ケンブリッジ大学)  特別推進

    Project Year :

    2008
    -
    2009
     

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    研究結果:日英の重力理論および宇宙論研究の第一線で活躍する研究者が、素粒子統一理論から予言される高次元宇宙における宇宙論を基礎に宇宙論の諸問題解明に取り組んだ。

  • ブレイン重力と宇宙論

    二国間交流事業(日本・ポーツマス大学)  二国間交流事業(日本・ポーツマス大学)

    Project Year :

    2005
    -
    2007
     

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    2000年に始まったブレイン宇宙論の研究を、この分野の第一線で活躍している日英の研究者を集め集中的に行った。期間中に行ったワークショップにおいては、次代の宇宙論としての可能性を探った。

  • Radio Observation in High Energy Astrophysics

    Project Year :

    2002
    -
    2005
     

     View Summary

    In Nasu Observatory, Radio Transient Sources were discovered with spherical dish array at 1.4GHz. These discoveries were investigated in the following Journals. In X and Gamma-ray astronomy as well as in optical astronomy, we have facilities having large field of view to detect transient objects. One example was Gamma-ray Bursts. It took more than 30 years to understand they were cosmological objects. In radio waves, transient sources in Galactic plane were known in early seventies. Typical one was Cyg-X3, in which large outbursts were observed once a year or so. However, no radio transients was known at high Galactic latitudes until Nasu Observatory started observation in 2000. We have developed Large Spherical Dish Array Interferometer at very low cost. We also developed digital signal processing system to search large field of view. As a result, we found several radio transients at high Galactic latitudes.

  • 複雑系の解明と新技術の開発

    文部科学省 

    Project Year :

    1999
    -
    2003
     

  • 複雑系の解明と新技術の開発

    文部科学省 

    Project Year :

    1997
    -
    2001
     

  • 素粒子・宇宙実験用希ガス液体検出器の開発

    文部科学省 

    Project Year :

    1997
    -
    2001
     

  • Inflation as an Attractor in Dynamical System and the Isotropy and Homogeneity of the Universe

    Project Year :

    1988
    -
    1989
     

     View Summary

    In this research, we investigated the problems on the generality of inflation, by which we can believe the present homogeneity and isotropy of the Universe, and found the following results.
    1. The main theme in this research is whether the universes which were created anisotropically or inhomogeneously call evolve into the present universe through inflation. As for this problem, we clarified the followings: (1) For the homogeneous but anisotropic universe, we know that any spacetimes except for Bianchi type IX always approach the inflationary solution. For Bianchi type IX spacetime, however, the results depend on the initial conditions of the universe, hence we showed from the quantum cosmological point of view that initial conditions which drive the universe into inflation are quite natural. (2) As for inhomogeneous spacetimes, we adopted two methods: (i) Two analytic approaches for symmetric spacetime: one is the so-called "inverse scattering method", and the other the Israel's thin shell method. In both case, we obtained inhomogeneous solutions with a cylindrical or plane- symmetry in de Sitter background, discussing about the cosmic no-hair conjecture. (ii) Numerical Approach for most general three-dimensional spacetime We first calculated a spherically symmetric case, and then started to study the most general three-dimensional case. We developed a new formalism, which will be convenient to simulate the cosmological model in the context of numerical relativity. We discussed how to choose a time slicing in the universe and also found a general solution for the linearized gravitational waves in de Sitter background, discussing the homogenization mechanism of inhomogeneities of spacetimes.
    2. The unified theories of the fundamental interactions may predict a modification of the Einstein theory at the high energy scale. A quantum corrections provide higher-derivative terms of the metric tensor and a non-minimal couping to scalar fields. Brans-Dicke type theories may be derived from higher-dimensional theories such as a superstring. We investigated whether inflation is a natural phenomenon even in such a generalized Einstein theory. Applying a conformal transformation of the metric tensor, we find that most theories are equivalent to the Einstein theory. Using this equivalence, we found that inflation is a natural phenomenon in most cases.

  • Creation and Evolution of Nonlinear Inhomogeneous Spacetime Structures and Numerical Cosmology

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    In this research, we discussed the problems on inhomogeneity of the Universe, in particular, on creation and evolution of inhomogeneous spacetime.1. The one of main topics in this research is whether the inhomogeneous universes evolve into the present universe through inflation. In order to investigate this subject, we first presented a formalism of numerical cosmology, which is a natural extension of numerical relativity for gravitational collapse.(1) We found the following two results :(i) Goldwirth and Piran calculated 1 dimensional spherically symmetric case, while we discussed 1 dimensional planar symmetric spacetime with cosmological constant in order to discuss inhomogeneity due to gravitational waves. We found that all spacetime evolve into de Sitter space. This strongly supports the cosmic no-hair conjecture.(ii) From our simulation and by an analysis of exact solutions, we proposed "Cosmic Hoop Conjecture" by which we can discuss on an inflationary scenario for general inhomogeneous spacetime.(2) For the homogeneous but anisotropic universe, we generalized Wald's theorem for the case of power-law inflation, which may be realized in generalized einstein theories discussed below.2. We also considered cosmology in generalized Einstein theories (GETs) such as Brans-Dicke theory. :(1) Although new and chaotic inflation need a fine-tuning in coupling constants, if we consider those in GETs, then such constraints is loosened. We call this model soft inflation.(2) In extended inflation, nucleated bubbles produce inhomogeneity of the Universe. The original model seems to be excluded from observation by a rough analysis of bubble expansion. However, we found by a detailed analysis that bubbles are nucleated in the Hawking-Moss mode instead of the Coleman-De Lucia mode, and the thin wall approximation is broken in an initial stage of inflation. This may change a scenario of the extended inflation model.(3) The structure formation in the Universe is one of the most important topics in cosmology, but no one knows yet what is a real mechanism. Using GETs, we looked for a new mechanism. In particular, we considered the theory with non-minimal coupling, which predicts an oscillation in Hubble parameter and then provides us a slow expanding phase of the Universe. We, hence, expect a rapid growth of the density perturbations in the slow expansion phase. For some parameters, we really found a large enhancement of the density perturbations. Unfortunately, the Universe must had an unphysical era in the past, when the effective gravitational constant was negative

  • 一般相対論における非線型動的現象と重力波

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    重力波を含めた一般相対論における非線型動的現象の研究は、方程式の非線型性のため解析的アプローチにおいては、従来、問題個々に限られた範囲でのみ考察されていた。そのいくつかは非常に興味深にもので、非線型物理学としての一般相対論は一部確立されている(逆散乱法を用いた解の生成法、膨張宇宙でのソリトン解、宇宙初期やブラックホールのまわりの粒子のカオス的振舞いなど)。しかし解析的にアプローチするには限界があり、その限界を数値的相対論を使って越えようとしたり解析的アプローチと数値的相対論との融合により、一般相対論の基礎的研究を行うという試みはいまだかってあまり行われておらず、それを重力波の動的振舞いに焦点をしぼり系統的に行うというのが本研究の特徴である。現在までに、おもに京都グループと共同で、膨張宇宙における重力波の非線型振舞いについて研究を行っている。重力波は、それ自身ブラックホールを形成するほどにその非線型性が大きくなりうるが、逆に宇宙膨張はその形成を妨げようとする。その競合過程を研究することで、重力波の非線型的性質、振舞い等についてより深い理解が出来ると考えられる。またこの研究は、宇宙論におけるインフレーションの必然性の議論においても重要になり、我々のこれまでの研究で、非一様な初期宇宙の進化についてかなり多くのことが明らかになった。さらに、我々は、現在世界的に活躍している日本人相対論研究者と相互に連絡をとり、本研究課題を拡張したテーマで「一般相対論と重力」研究会をスタートしている。本年度は、93年1月に早稲田大学で開催した。参加者は予想を上回り140名以上で、多くの若手研究者の参加、研究発表(60講演)があり、この分野の研究会としては盛況なものになった。これらの成果は英文の報告集としてまとめられている。この研究会をきっかけとして、さらに多くの研究者がこの重点領域研究に興味を持ち、重点領域推進の一助となることが期待され、そのためにも、今後も年一回の研究会を開催する予定である

  • Physical Procession in the system with cosmological constant and dynamics of in homogeneous space-times

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    We investigate dynamics of inhomogeneous spacetime with a cosmological constant and find a universal picture : There is a critical value of the Abbott-Deser mass, beyond which localized inhomogeneities do not collapse into black holes. Consequently, black holes with large mass cannot be formed in the asymptotically de Sitter space-time, unless a naked singularity is formed. This result suggests a possible inflationary scenario for inhomogeneous universes

  • 一般相対論における非線型動的現象と重力波

     View Summary

    重力波を含めた一般相対論における非線型動的現象の研究は、方程式の非線型性のため解析的アプローチにおいては、従来、問題個々に限られた範囲でのみ考察されていた。そのいくつかは非常に興味深にもので、非線型物理学としての一般相対論は一部確立されている(逆散乱法を用いた解の生成法、膨張宇宙でのソリトン解、宇宙初期やブラックホールのまわりの粒子のカオス的振舞いなど)。しかし解析的にアプローチするには限界があり、その限界を数値的相対論を使って越えようとしたり解析的アプローチと数値的相対論との融合により、一般相対論の基礎的研究を行うという試みはいまだかってあまり行われておらず、それを重力波の動的振舞いに焦点をしぼり系統的に行うというのが本研究の特徴である。現在までに、おもに京都グループと共同で、膨張宇宙における重力波の非線型振舞いについて研究を行っている。重力波は、それ自身ブラックホールを形成するほどにその非線型性が大きくなりうるが、逆に宇宙膨張はその形成を妨げようとする。その競合過程を研究することで、重力波の非線型的性質、振舞い等についてより深い理解が出来ると考えられる。またこの研究は、宇宙論におけるインフレーションの必然性の議論においても重要になり、我々のこれまでの研究で、非一様な初期宇宙の進化についてかなり多くのことが明らかになった。さらに、我々は、現在世界的に活躍している日本人相対論研究者と相互に連絡をとり、本研究課題を拡張したテーマで「一般相対論と重力」研究会をスタートしている。本年度は、93年1月に早稲田大学で開催した。参加者は予想を上回り140名以上で、多くの若手研究者の参加、研究発表(60講演)があり、この分野の研究会としては盛況なものになった。これらの成果は英文の報告集としてまとめられている。この研究会をきっかけとして、さらに多くの研究者がこの重点領域研究に興味を持ち、重点領域推進の一助となることが期待され、そのためにも、今後も年一回の研究会を開催する予定である

  • Theoretical Study of General Relativity and Gravetational Waves

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    Because of recent important observations and experiments of gravity or progress of computer science, we are now in the most exciting epoch of general relativity and gravitation after Einstein's theory of general relativity. Taking this opportunity, we had planned a systematic collaboration for several important subjects on relativity and gravity by prominent researchers. The subjects we studied are classified into three categories :(1) Fundamental problems in general relativity and gravitational wave astronomy (analytic approach : T.Futamase, K.Maeda, T.Nakamura, M.Sasaki, A.Tomimatsu ; numerical approach : Y.Eriguchi, H.Ishihara, Y.Kojima, T.Nakamura, K.Oohara, H.Shinkai)(2) Fundamental problems in relativistic cosmology (T.Futamase, A.Hosoya, Y.Kojima, K.Maeda)(3) Fundamental problems in particle physics and gravity (H.Ishihara, H.Kodama, K.Maeda, M.Sasaki, A.Tomimatsu, M.Yoshimura)In addition, we held three conferences on general relativity and gravitation each year for all researchers in this field to get together and to have discussions. For each conference, the number of participants was about 150 and we had beyond 50 talks. The results are published in the proceedings in Englishi. We also had several workshops by small numbers of researchers and students to make intensive discussion and collaborations

  • 一般相対論における非線型動的現象と重力波

     View Summary

    重力波を含めた一般相対論における非線型動的現象の研究は、方程式の非線型性のため解析的アプローチにおいては、従来、問題個々に限られた範囲でのみ考察されていた。そのいくつかは非常に興味深にもので、非線型物理学としての一般相対論は一部確立されている(逆散乱法を用いた解の生成法、膨張宇宙でのソリトン解、宇宙初期やブラックホールのまわりの粒子のカオス的振舞いなど)。しかし解析的にアプローチするには限界があり、その限界を数値的相対論を使って越えようとしたり解析的アプローチと数値的相対論との融合により、一般相対論の基礎的研究を行うという試みはいまだかってあまり行われておらず、それを重力波の動的振舞いに焦点をしぼり系統的に行うというのが本研究の特徴である。現在までに、おもに京都グループと共同で、膨張宇宙における重力波の非線型振舞いについて研究を行っている。重力波は、それ自身ブラックホールを形成するほどにその非線型性が大きくなりうるが、逆に宇宙膨張はその形成を妨げようとする。その競合過程を研究することで、重力波の非線型的性質、振舞い等についてより深い理解が出来ると考えられる。またこの研究は、宇宙論におけるインフレーションの必然性の議論においても重要になり、我々のこれまでの研究で、非一様な初期宇宙の進化についてかなり多くのことが明らかになった。さらに、我々は、現在世界的に活躍している日本人相対論研究者と相互に連絡をとり、本研究課題を拡張したテーマで「一般相対論と重力」研究会をスタートしている。本年度は、93年1月に早稲田大学で開催した。参加者は予想を上回り140名以上で、多くの若手研究者の参加、研究発表(60講演)があり、この分野の研究会としては盛況なものになった。これらの成果は英文の報告集としてまとめられている。この研究会をきっかけとして、さらに多くの研究者がこの重点領域研究に興味を持ち、重点領域推進の一助となることが期待され、そのためにも、今後も年一回の研究会を開催する予定である

  • Black Hole in Particle Physics and its Cosmologicul Implication

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    We have analyzed a property and stability of new type of black holes, which do not belong to the Kerr-Newman family. In a unified theory of fundamental interactions, we usually expect non-Abelian gauge fields, which provide us new types of non-trivial structure like a monopole and new black holes. We have classified those black holes and presented a unified picture. We have also shown that the stability of those black holes is understood by a catastrophe theory, when the entropy of a black hole is regarded as the potential function.The qunatum radiation process of black holes has also been studied in theories with a dilaton field, which is inspired by a unified theory. A superstring model turns out to be critical in a sense that the energy flux of Hawking radiation diverges if the dilaton coupling with U (1) gauge field is larger than that of the superstring model

  • Cosmological Constant and the Evolution of the Universe

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    1) Neutrino Background Radiation due to Supernove ExplosionRecently Superkamiokande project has started and it can observe the relic neutrino through supernove explostion. We investigated carefuly the spectrum of relic neutrino using the model for the chemical evolution of galaxies. The total flux depends strongly on the Hubble parameter, but weakly on the cosmological constant. We found that in the same flat universe model the flux in lambda=0 is smaller than that in lambda*o.2) Primordial NucleosynthesisThe primordial nucleosynthesis is best tool for deciding the baryon density. Recently, associated with the progress of techonology in obsevational field, the obsevational result pointed out that the simple model for cosmology has a trouble point. Some of people call the problem as 'crisis' in the universe. Hence, we taken account of the theoretical error in the lepton asymmetry universe and estimeted statistically the final fraction of the light elements by Monte Calro simulation. The result is that the best values for the degenerate parameter and the baryon density are 0.043(]SY.+-。[)0.040 and 0.015(]SY.+-。[)0.006-0.003 (CL.95 percent)

  • 5次元ディジタル信号処理によるパルサーサーベイと重力理論の検証

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    (ナイキストレートでの空間時間FFT)世界ではじめて、ナイキストレートで処理を行う空間時間FFTプロセッサーを開発し(Daishido,T.et al,2000)、64台のアンテナからなる干渉計に接続して、64方向、256チャネル同時観測を実現した。(信号の流れのトポロジー)このプロセッサーの開発・製作過程では多くの工夫がなされ、世界に新しい流れをつくりだした。第一は、空間処理FFTと時間処理FFTの信号の流れのトポロジーが全く同じであることを積極的に利用して、全く同じ構造のプロセッサー2組で空間時間FFTを一挙に実現したことである。(空間時間データの並べ換え)間に設置した空間時間データ変換部の設計には、大いに頭をしぼったが、完全に作動し、見通しの正しかったことが確認できた。実際、空間FFTの基板と時間FFTの基板を交換しても動くことを確かめてある。このことにより、メインテナンスが楽になり、製作経費が低く押さえられた。トポロジーは同じであるが、FFTのバタフライ演算に設定する位相回転子はもちろん異なる。(Radix-4 FFT バタフライLSIの設計)設計の主要部分は研究室が関わり、Radix-4演算を行うLSIの設計は、博士課程在学中の田中(Tanaka,N.et al,2000)が中心に行った。空間16×16、時間256、のFFTのトポロジーが同一なので、ハードウエアとしては同一のプリント基板を使い、空間FFT(16枚、2ブロック)、時間FFT(16枚2ブロック)で構成し、中間のST変換部でデータの並べ換えを行う。基板の総数は、64枚となる。各基板は、16複素入力、同出力、となるので、バタフライLSIは、初段に4個、2段目に4個の計8個が実装される。LSIの総数は、8×64=512個となり、カスタムLSI(ASIC)で製作した。数が多いのでFPGAで構成するときの1/10のコストで実現できた

  • Studies on general-relativistic astrophysical phenomena

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    In this study project we covered the general-relativistic astrophysical phenomena on all space-and-time scales of the Universe and tried to clarify their mutual connections. The studies were performed for 4 years from 2000 to 2003 fiscal year, and many valuable results were obtained. They are classified into three groups : (1) the space-time structure at the very early stages in the neighborhood of the big-bang, (2) phenomena on spatially small scales (gravitational waves, high density stars and black holes), and (3) phenomena on spatially large scales (the non-uniformity, large-scale structures and gravitational lensing). In each of them, the remarkable results are that (1) theories on the multidimensional brane world and our Universe as its four-dimensional section were introduced and studied extensively, (2) the framework of gravitational-wave astrophysics was constructed and the formation mechanism of gamma-ray bursts began to be clarified, and (3) various cosmological observations (like WMAP, SDSS etc) were executed, the cosmological model parameters were determined assuming the cosmological principle and the existence of dark energy was clarified. Many of these results were reported in the Workshops of General Relativity and Gravitation held in Osaka University, Waseda University, University of Tokyo and Osaka City University, and in Workshop of "Frontiers of Cosmology and Gravitation" as well as the other international conferences. These Workshops and conferences were useful for the international communications and the education of young physists in our field

  • 相対論的力学系の物理と重力波天文学

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    重力波は,重力場の時間変化,つまり物体の運動によって引き起こされるが,強い重力場を伴う現象でないと重力波観測のための源として期待できない.そこでまず重要となる課題は,相対論的力学系における物体運動の解析である.その解析で最も簡単な方法がテスト粒子近似であるが,そのような場合でも系の非可積分性からカオスなどの力学系特有の非線型現象が現れる.実際,回転するカーブラックホールの周りを運動するスピンをもった粒子の運動はある状況でカオス的に振る舞うことが申請者たちによって示されている.その研究を元に,J.Levin博士は一般の連星系においても同じようなカオス的振る舞いが見られ,それが重力波観測に影響することを指摘している.一方,Schnittman博士とRatio博士らの解析ではリャプノフ指数が小さく,合体するときにはカオスが起こる十分な時間がないことを示している.しかし,赤道面を離れた場合のような3次元的な物体運動においてはその多くが明らかにされていない.そこで本研究では,相対論的な力学系(質点+ディスク系およびカー時空のまわりのスピン粒子)を系統的に解析し,系の非線形現象の解明と,それに伴う重力波の研究を行った.特に,粒子がカオス的振る舞いをする場合とそうでない場合の放出重力波の性質(波形.スペクトルなど)のどの部分に違いが現れるかを解析し,観測される重力波から系の運動状態が予測可能かどうか考察した。その結果,カオス的振る舞いをしない系ではエネルギースペクトルにおいて特徴的な波数が存在するのに対し,カオス力学系からの重力波のエネルギースペクトルにはすべての波数の波が出現することがわかった.また,これらの解析を元に相対論的力学系一般における重力波の性質及び役割を明らかにすることができる

  • Relativistic Astrophysics Based on Brane Cosmologyブレイン宇宙モデルに基づく相対論的宇宙物理学

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    The idea of "brane", which appeared in string theory, changes completely the view of the early universe and strong gravitational phenomena. It also changes the view of higher dimensions from the conventional old idea by Kaluza and Klein, i.e., the existence of a brane makes a large extra dimension possible and visible. Furthermore new brane models proposed by Randall and Sundrum give new types of compactification mechanism. Especially, the second model has become the focus of cosmologist's attention because it gives the Newtonian gravity in higher dimensional world without compactification. This model provides definitely a different aspect from the conventional Kaluza-Klein compactification. Hence many relativists and cosmologists are studying it to look for new world view. Under such a circumstance, it is very important to analyze cosmological models and strong gravitational phenomena such as a black hole or gravitational collapse based on this brane gravitational theory. In this research project, we study new view of the brane world with the help of two prominent young professors (David Wands and David Langlois).In order to clarify the properties of brane gravity, we have studied brane collision in the ekpyrotic cosmological model, which could be an alternative of the standard inflation scenario, and the reheating mechanism, which leads the universe to a big bang. We have also analyzed some effective theories with higher curvature terms, which come from quantum correction of string theory discussed their cosmological models, and proposed new inflationary scenario

  • Brane Gravity and Fundamental Problems in Cosmology

     View Summary

    New idea of gravitation is given from a "brane" in string theory, and it has recently been intensively studied because it may lead to new paradigm of cosmology. In the present research project, we have analyzed systematically fundamental problems in cosmology from the view point of a brane world in order to study new subjects such as what is the fundamental and important in brane gravity or what will be new paradigm of brane cosmology. Especially, studying new gravitational theory with a brane, we have discussed most important subjects in cosmology such as "dark energy", "cosmological constant problem", "creation of the universe" and "cosmological singularity". We have analyzed mainly the following three subjects:(1) The study of the unconventional early universe models based on brane collisionTaking into account self-gravity, we have analyzed a brane collision and shown that a spacetime singularity is formed because of gravitational instability. We have also studied the possibility of creation of matter (the origin of matter) in the universe via a brane collision.(2) The study of the inflation models based on string theoryWe have proposed new inflationary model based on string theory. We have studied the higher curvature terms which appear via quatum corrections in superstring theory. Although we find sufficient expansion of the universe, we need a fine tuning of initial conditions. It suggests that we have to find the proper correction terms with the Ricci curvature tensor as well as the Riemann one.(3) The construction of black hole solutions based on string theoryWe have presented new method to find black hole solutions in string theory. It is generalization of the conventional method using the BPS equations. We have obtained a new black hole (a caged black hole) solution

  • dark energy and gravitational theory

     View Summary

    We study the so called "dark energy problem", which is one of the most important subjects of modern cosmology, from three approaches : (1) exotic fluid of dark energy (2) modified gravity theories (3) the possibility of other natural models. We have pointed out that it is important to analyze a strong gravitational system such as a black hole or a neutron star which is coupled to dark energy

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Presentations

  • Metric-Affine Gravity Theory and Inflation

    Kei-ichi Maeda  [Invited]

    Workshop on COSMOLOGY AND THE QUANTUM VACUUM  (Benasque) 

    Presentation date: 2018.09

  • Metric-Affine gravity theory and acceleration of the Universe

    Kei-ichi Maeda  [Invited]

    5th Korea-Japan joint workshop on Dark Energy at KMI  (Daejeon) 

    Presentation date: 2018.08

  • Massive Graviton Geons and Dark Matter

    Kei-ichi Maeda

    Workshop on Frontiers in Gravitation, Astrophysics, and Cosmology (ICNFP 2018)  (Creta) 

    Presentation date: 2018.07

  • Massive Graviton Geon in Bigravity Theory

    Kei-ichi Maeda  [Invited]

    Fifteenth Marcel Grossmann Meeting MG15  (Rome) 

    Presentation date: 2018.07

  • Black Holes in the Universe from Higher Dimensions

    Kei-ichi Maeda  [Invited]

    Brinsop Meeting for Stephen Hawking  (Brinsop) 

    Presentation date: 2017.09

  • Matter coupling and the coincidence problem

    Kei-ichi Maeda  [Invited]

    4th Korea-Japan joint workshop on Dark Energy at KMI  (Nagoya University) 

    Presentation date: 2017.08

  • Inflation and Disformal Transformation

    Kei-ichi Maeda  [Invited]

    International Conference on Gravitation : Joint Conference of ICGACXIII and IK15  (Seoul) 

    Presentation date: 2017.07

  • Inflation and Disformal Transformation

    Kei-ichi Maeda  [Invited]

    The 2017 Annual meeting of the Division of Gravitation and Relativistic Astrophysics of the Chinese Physical Society / The Fifth Galileo-Xu Guangqai Meeting 

    Presentation date: 2017.06

  • Chaotic dynamics of a classical string on AdS black hole spacetime

    Kei-ichi Maeda  [Invited]

    Black Hole New Horizons  (Oaxaca) 

    Presentation date: 2016.05

  • The Use of Disformal Transformation

    Kei-ichi Maeda  [Invited]

    3rd Korea-Japan Workshop on Dark Energy  (Daejeon) 

    Presentation date: 2016.04

  • 一般相対性理論と宇宙論

    前田恵一  [Invited]

    日本物理学会「秋季大会」大阪市大  (大阪) 

    Presentation date: 2015.09

  • Relativistic Stars in Bigravity Theory

    Kei-ichi MAEDA  [Invited]

    2nd APTCP-TUS workshop on Dark Energy  (Tokyo) 

    Presentation date: 2015.08

  • Dark energy and dark matter in the ghost-free bigravity theory

    Kei-ichi MAEDA  [Invited]

    Fourteenth Marcel Grossmann Meeting, University of Rome  (Rome) 

    Presentation date: 2015.07

  • The origin of scalar fields and their roles in cosmology

    Kei-ichi MAEDA  [Invited]

    Fourteenth Marcel Grossmann Meeting, University of Rome  (Roma) 

    Presentation date: 2015.07

  • Black Hole Shadow

     [Invited]

    Presentation date: 2014.10

  • Time-dependent black holes from higher dimensions

    Kei-ichi Maeda  [Invited]

    KITPC workshop on Quantum Gravity, Black Holes and Strings  (Beijing) 

    Presentation date: 2014.07

  • Cosmology in bigravity theory

    Kei-ichi MAEDA  [Invited]

    The APCTP-TUS workshop on "Dark Energy"  (Pohang) 

    Presentation date: 2014.06

  • Gravitational lensing and black hole shadow

    Kei-ichi Maeda  [Invited]

    SYMPOSIUM ON GRAVITY AND LIGHT,  (Kavli IPMU, University of Tokyo) 

    Presentation date: 2013.10

  • Dynamics of bigravity and general relativity

    Kei-ichi Maeda  [Invited]

    Les Rencontres du Vietnam Hot Topics in General Relativity and Gravitation  (Quy Nhon) 

    Presentation date: 2013.07

  • Anisotropic universes in bigravity theory and homothetic metrics

    Kei-ichi Maeda  [Invited]

    Mini-workshop "Massive gravity and its cosmological implications,  (Kavli IPMU, University of Tokyo) 

    Presentation date: 2013.04

  • Inflation with Gauge Fields

    Kei-ichi Maeda  [Invited]

    Workshop Cosmology Montpellier12  (Montpellier) 

    Presentation date: 2012.10

  • Accelerating Universe in Effective String Theory

    Kei-ichi Maeda  [Invited]

    Accelerating Universe in Effective String Theory, Ginzburg Memorial Conference  (Moscow) 

    Presentation date: 2012.05

  • Field Redefinition and the Observed Universe

    Kei-ichi Maeda  [Invited]

    Workshop on Testing Gravity with Astrophysics and Cosmological Observations,  (IPMU,Tokyo) 

    Presentation date: 2012.01

  • Black holes in an expanding universe

    Kei-ichi Maeda  [Invited]

    BIRS workshop on Black Holes: New Horizons, 2011.11.23,  (Banff) 

    Presentation date: 2011.11

  • Anisotropic spacetime in Horava-Lifshitz gravity

    Kei-ichi Maeda  [Invited]

    Chinese conference on gravity and cosmology  (Shanxi) 

    Presentation date: 2011.08

  • Time dependent black holes from higher dimensions

    Kei-ichi Maeda  [Invited]

    IPMU Workshop on Black Holes  (IPMU, Tokyo) 

    Presentation date: 2011.02

  • Dimenional Reduction

    Kei-ichi Maeda  [Invited]

    The 20th Workshop on General Relativity and Gravitation in Japan - JGRG20  (Kyoto) 

    Presentation date: 2010.12

  • Time-dependent Black Hole from Higher Dimensions

    Kei-ichi Maeda  [Invited]

    APCTP conference on Frontiers of Black Hole Physics  (Pohang) 

    Presentation date: 2010.12

  • Black Holes in and from Higher Dimensions

     [Invited]

    Presentation date: 2009.12

  • Cosmology and black holes in string theory

    Kei-ichi Maeda  [Invited]

    New topics in Modern Cosmology, Spontaneous Workshop II  (Cargese) 

    Presentation date: 2009.05

  • Time-dependent Black Holes in Supergravity Theories

    Kei-ichi Maeda  [Invited]

    Black Holes VII, Theory and mathematical aspects  (Banff) 

    Presentation date: 2009.05

  • Cosmology in Higher Dimensions

    Kei-ichi Maeda  [Invited]

    The 7th RESCEU International Symposium on Astroparticle Physics and Cosmology  (Tokyo) 

    Presentation date: 2008.11

  • Beyond the Einstein-Hilbert Action

    Kei-ichi Maeda  [Invited]

    The 6th INTERNATIONAL CONFERENCE on GRAVITATION & COSMOLOGY (ICGC-07)  (IUCAA, Pune) 

    Presentation date: 2007.12

  • Collision of Domain Walls and Matter Creation in Brane World

    Kei-ichi Maeda  [Invited]

    International Workshop on String Theory and Cosmology  (Beijing) 

    Presentation date: 2007.11

  • Black Holes in Superstring Theory

    KIAS-YITP joint, workshop on String phenomenology, cosmology  [Invited]

    (Kyoto) 

    Presentation date: 2007.09

  • Collision of Domain Walls and Creation of Matter in Brane World

    Kei-ichi Maeda  [Invited]

    The 8-th ICGA on Gravitation and Astrophysics  (Nara) 

    Presentation date: 2007.08

  • Collision of Domain Walls and Creation of Matter in Brane World

    Kei-ichi Maeda  [Invited]

    Workshop on Frontiers of Black Hole Physics  (Pohang) 

    Presentation date: 2007.06

  • Collision of domain walls and brane world

    Kei-ichi Maeda  [Invited]

    APCTP-TPI Meeting on Gravity, Cosmology, and Astrophysics  (Alberta) 

    Presentation date: 2006.12

  • Collision of domain walls and brane world

    Kei-ichi Maeda  [Invited]

    Conference on High Energy, Cosmology and Strings  (Paris) 

    Presentation date: 2006.12

  • Collision of domain walls and matter in brane-world

    Kei-ichi Maeda  [Invited]

    Brane-World and Gravity -- Progress and Problems  (Portsmouth) 

    Presentation date: 2006.09

  • Collision of Thick Branes

    Kei-ichi Maeda  [Invited]

    Cambridge-Mitchell Texas Conference  (Cambridge) 

    Presentation date: 2006.08

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Specific Research

  • 重力波天文学に向けた相対論的三体系のダイナミクスと重力波

    2020  

     View Summary

    連星合体からの重力波直接観測により、新しい天文学としての重力波天文学は物理学や天文学に大きな寄与をする段階になってきた。この段階において、理論物理学として重要な課題は、観測可能な重力波源の詳細な解析で、現在発見されている連星以外の重力波源はさらに新たな情報をもたらすと期待される。申請者は、階層的3体系のダイナミクスの解析を行い、そのような系からの放出重力波について詳細に調べた。その結果、現在計画されているLISAなどによる観測可能性を指摘した。また、Lense-Thirring効果が重要となるブラックホールが回転している場合についての解析も行い、その重要性を指摘した。

  • 三体力学系のダイナミクスと重力波

    2019  

     View Summary

    自然界には連星のような2体系以外にも3体や4体の力学系が数多く存在する。そのような系は非可積分系で、カオスなど従来にない振る舞いを示すため、そのような系からどのような重力波が放出されるかを解析しておくことはこれからの重力波天文学にとって非常に重要である。本研究では、3体系でも比較的規則正しく運動する階層的3体系からの重力波についての研究を行った。この階層的3体系においては、古在・リドフ機構と呼ばれる重要な効果が現れ、内部連星軌道の離心率が周期的に変化する。特に、その離心率が大きくなるフェイズで重力波放出量が非常に大きくなり、LISAなどの宇宙空間における観測計画で観測可能となることを示した。

  • 相対論的重力系における重力波と修正重力理論の研究

    2018  

     View Summary

    2015年9月の重力波の発見により本格的に始まった重力波天文学においては、相対論的力学系からの重力波の理論的な解析が重要な役割を担っている。本研究では階層的三体系における重力波について解析を行った。階層的三体系はより近くを回る連星(内連星)と第3の天体が連星系(外連星)をなす系である。その系に特徴的な古在・リドフ振動は、内連星および外連星のそれぞれの回転面のなす角と内連星の離心率の間の振動である。本研究では、離心率が大きくなったときにより多くの重力波を放出し、近星点移動の累積変化曲線が大きく曲がることを明らかにした。この変化が観測されれば、一般相対性理論のさらなる検証を与えることになる。

  • AdS/CFT対応におけるブラックホール時空とカオス

    2017  

     View Summary

    本研究では、AdS/CFT対応を研究する際に重要となる重力サイドの漸近的AdS時空のダイナミクスとして特に「AdS時空上におけるカオスなどの非線形動力学系」に着目し、漸近的AdSブラックホール時空における弦の振る舞いについて研究を遂行した。従来ほとんど議論されてきていないAdS時空におけるカオス力学系を研究することはAdS/CFT対応における研究の基礎の一つを与える。本研究遂行のために、重力物理学の権威であるGibbons教授と議論するために2017年9月にCambridge大学を訪問した。また、宇宙論・カオス力学系研究の第一人者であるBarrow教授と情報交換を行い、新しく共同研究をスタートした。

  • AdS/CFT対応の基礎としてのブラックホール動力学

    2016  

     View Summary

    昨年度に引き続き、本年度も、AdS/CFT対応研究に重要な漸近的AdS時空のダイナミクスの研究を行った。本研究では、特に「AdS時空上におけるカオスなどの非線形現象」に着目し研究を遂行した。SchwarzschildAdS&nbsp;時空に於ける弦の運動について解析を行い、&nbsp;winding数が異なる場合には非可積分になり、特に質量が臨界値を越えると強いカオス性を示すことを明らかにした。さらにその量子系における解析を行い、可積分系と非可積分系における準位間隔分布の差について解析を行い、弦の量子論における基礎的問題を提起している。

  • AdS/CFT対応に基づく物理学の基礎的問題へのアプローチ

    2015  

     View Summary

    本研究では、AdS/CFT対応を研究する際に重要となる重力サイドの漸近的AdS時空のダイナミクスに特化して研究を遂行した。従来の時空のダイナミクスとは異なる新しい展開が期待できるものとして「AdS時空上におけるカオスなどの非線形現象」があるが、本研究では、Schwarzschild AdS 時空に於ける弦の運動について解析を行い、&nbsp;winding数が異なる場合には非可積分になり、特に質量が臨界値を越えると強いカオス性を示すことを明らかにした。これらの成果は学術論文として準備中である

  • 重力波天文学に向けたbigravity理論における重力波研究

    2014  

     View Summary

    本特定課題研究では、現代宇宙論最大の謎であるダークエネルギー問題に関して、重力子に質量を持たせるmassive gravity 理論を拡張したbigravity理論を基礎に解析した。その中でも特に、第二の計量と結合する「双子物質」に着目し、我々の宇宙のダークマターとして振る舞う可能性を精査し、ダークマターの3つの必要条件(銀河の回転曲線、構造形成問題、宇宙の構成要素)すべてを満たすことが出来ることを示した。タイトルにあるbigravity理論における重力波に関しては,現在研究が進行中である。

  • 重力波天文学と重力理論の検証

    2012  

     View Summary

    1990年代半ばから始まった大型重力波望遠鏡建設計画は、米国のLIGO、欧州のVIRGOの観測開始,そして日本のKAGRA計画の実質的スタートにより本格的観測が可能な段階に突入し、重力波天文学は現実的なものになってきている。この重力波天文学の重要な目的としては,重力理論の検証,超高密度領域における新しい現象の探求,そして第3の目としての天文学である。一方、ビッグバン標準宇宙論の大成功にもかかわらず、宇宙論では「ダークエネルギー」という大きな謎が出現し、人類は新たな挑戦状を突きつけられている。宇宙の4分の3が宇宙膨張を加速させる未知のエネルギーで占められているという。その正体はまだ全くわかっていないが、一つの可能性として、宇宙規模のスケールでは一般相対性理論が変更を受け、それに代わる新しい重力理論により加速膨張を説明しようというアプローチが提案されている。このような状況においては、重力波天文学の目標の一つである「重力理論の検証」を相対論研究の立場からより真剣に考える必要がある。本研究では、申請者のこれまでの種々の重力理論研究の経験を生かし、そのような新しい重力理論に基づく重力波の研究を行う。その具体的方法および成果は以下の通りである。ダークエネルギーを説明する新しい重力理論としては、量子補正などから期待される曲率高次の項を現象論的に取り入れたf(R)重力理論、基礎方程式が2階微分方程式で表されるガリレオン重力理論、また一般相対性理論の代替理論として従来から研究されているBrans-Dicke 理論やスカラー・テンソル理論、ベクトル場を加えたアインシュタイン・エーテル理論やTeVeS理論、さらには、有限質量の重力子を考える有質量重力理論(massive gravity)や双重力理論(bi-gravity)など、非常に多くの重力理論が提唱されている。本研究では、重力波を用いてそれらの理論を判別する方法としてブラックホールのQuasi Normal Mode(QNM)解析を考える。一般相対性理論において従来から研究されている連星系の合体やそれに伴うブラックホール形成から放出される重力波は重力波天文学の重要なターゲットの一つであるが、その最終段階で放出されるQNM重力波はブラックホールの性質に大きく依存する。ところが重力理論が異なるとブラックホール解やその摂動方程式が異なり、QNM重力波観測が重力理論検証に決定的な役割を果たすと考えられる。そこで、様々な重力理論に基づくブラックホール解の探索とそのQNM解析を目指した。まずその準備段階として、ブラックホール解は必ずしも解析的に得られるとは限らないので、数値解でブラックホールが得られた場合のQNMを求める手法を開発した。また、近年特に注目されている双重力理論においては、質量ゼロの重力子とともに有限質量の重力子が現れ、それが観測的に大きな制限を与えることが予想される。この場合のブラックホールはSchwarzschildまたはSchwarzschild-de Sitter時空で記述されるが、その場合のQNMがどのように得られ、観測的にどのような制限が加わるかという問題に関しては、まだ最終的な結果が得られていなく、近い将来にその研究成果を発表する予定である。

  • 自己重力系の統計力学と宇宙の構造形成

    2002  

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    本研究では,非線形物理学の観点から,重力多体系の動的性質について考察した.具体的には、次の二種類のモデルを詳しく解析した.1.まず背景時空は平坦な宇宙であるとして,その中で多くの一次元シートがニュートン重力によって相互作用を及ぼすモデルを解析し,宇宙で観測されるフラクタル構造の起源をさぐった.このシートモデルは解が解析的に記述できるため,長時間の発展を追う事ができる.膨張入りのシートモデルで初期密度ゆらぎをフラクタル的にした場合には,十分に時間が経過した後に非線形なフラクタル構造が形成されるが,そのフラクタル次元は,初期ゆらぎのフラクタル次元によらずほぼ普遍的な次元0.9に収束することがわかった.この普遍性は重力の長距離相互作用を反映したものと考えられる.また,このフラクタル構造は相空間にも特徴を持つ.自己重力により形成された構造はその相空間では渦巻き状の構造をすることが簡単な解析からわかるが,初期にフラクタル的揺らぎをしていると,構造形成後にはその渦巻き構造が入れ子構造をしていることがわかった.この成果を用いると,実際の観測データの解析により密度揺らぎの起源を特定化できる可能性を与える点で注目に値する.2.もう一つのモデルとして,三次元重力の特徴を備えた簡単なモデルを考案した.三次元重力と同じ形の相互作用を及ぼしあう多くの粒子を一次元リングに拘束したモデル(リングモデル)で,このモデルでは特定のエネルギー範囲では比熱が負になり,粒子が密集したコア層の周囲に特異な振る舞いを示すハロー粒子が取り巻くという,三次元重力の特徴が現れる.重力の特徴を解析する上で,このリングモデルは少ない計算量で高い解像度を得る事ができ,フラクタル構造が形成されるかどうかを調べる場合にも有用と考えられる.このモデルを詳細に解析した結果,非ガウス的な速度分布や粒子分布のスケーリング則の起源がガス層とコア層を行き来するハロー粒子の存在にあることを明らかにした.以上の研究により,重力などの長距離相互作用が働く多体系における統計的性質の重要な一面(つまり,フラクタル構造やその次元及び非ガウス的分布など重力多体系において特有に現れる普遍的性質)が明らかにされた.

  • 超ひも理論と時空の特異点

    1997  

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     ビッグバン宇宙論によると宇宙の始まりは特異点ということになり、そこでは一般相対論は何らかの変更が余儀なくされる。インフレーション宇宙論は、宇宙初期の標準モデルになりつつあるが、特異点問題は解決されない。量子宇宙論がその可能性として考えられるが、もう一つの鍵として素粒子の統一理論がある。統一理論としては、超ひも理論がもっとも有望ではあるが、その宇宙論的応用はまだ十分なものとはいえない。一方、ブラックホールにおいても、ホーキングが1973年にブラックホールの量子論的蒸発を示したが、その最終状態に関してはまだよくわかっていない。そこで、我々は、超ひも理論を基礎にした宇宙初期やブラックホールにおける特異点の振舞いに関し系統的な研究を行った。 超ひも理論では、高エネルギー極限で、通常のアインシュタイン理論とは異なる新しい量子的な効果として曲率高次の項が現れることが予想されている。そこで、我々はまず曲率2次の項として期待されるGauss-Bonnet 項が付加された場合の影響についてブラックホール及び初期宇宙論について特に特異点出現の観点から考察した。また、統一理論で現れるYang-Mills 場(非可換ゲージ場)を伴うブラックホールについても詳細に解析した。さらに宇宙項やディラトン(系に普遍的に現れるスカラー場)の影響についても考察を行った。その結果、これらの効果は必ずしも特異点回避には十分ではなく、特異点のタイプを変更するにとどまることを明らかにした。場の理論的取り扱いを超えたひも理論的な取り扱いの必要性を示唆している。

  • 相対論的力学系としての連星パルサーと重力波

    1996  

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     Hulse とTaylor の発見した連星パルサーによってその存在が明らかにされた重力波を直接観測しようと、LIGOを初めとする重力波干渉計の大型プロジェクトも着々と進み、21世紀初めには最初の重力波観測も夢ではなくなった。重力波は従来の電磁波や新しい観測手段のニュートリノでは観測できない星の最終段階や宇宙初期などを見る第3の目として期待されている。もし、その重力波を使った天文学が現実のものとなれば、天文学的重要性に加えて、物理学の基本的な問題にまで迫りうる重力波天文学が可能になる。特に、連星パルサーの合体は重力波源としても有望で、そのテンプレート制作は重力波天文学の理論的最重要課題で、世界各地で研究が続いている。 ところで、天体を記述する天体力学に関しては、ニュートン重力理論を基礎にした研究が非常に活発で、先駆的なポアンカレによる三体問題の研究はもちろん、最近ではコンピュータを使ったより定量的な解析が進み、そのような力学系を非線形物理学の一つの分野として議論するようになってきている。一方、連星パルサーの合体などで重要となるアインシュタインの重力理論は、複雑な非線形偏微分方程式で重力場自身も非線形となるので、ニュートン理論では現れない新しいタイプの非線形現象も期待できるが、その研究はこれまでほとんどなされていない。そのような非線形現象、特にカオスなどは連星パルサーの運動に大きな影響を与え、上記の重力波テンプレート作りの重要な要素となる可能性がある。そこで、本研究では連星パルサーの合体などの相対論的天体力学を念頭に置き、相対論的力学系における非線形現象について詳細に調べ、それが重力波観測計画に与える影響について考察した。その結果、どのような状況で連星パルサーの合体などから放出される重力波において、カオスなどの非線形現象が重要となるのかを明らかにした。また、本研究により、重力系における非線形現象の重要性を明らかにし、相対論的宇宙物理学に相対論的力学系という新しい分野が開拓できたものと思う。

  • 宇宙の構造形成問題の総合解析-その物理的素過程研究からのアプローチ

    1995   大場 一郎, 相沢 洋二, 大師堂 経明, 金長 正彦, 宮坂 朋宏

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    観測されている銀河や銀河団などの宇宙の大構造は現代科学における最も大きな謎の一つである。「COBEなどの観測衛星が明らかにした『凸凹のほとんどない宇宙初期』からいかに『現在の構造』ができたのか?」というのが『宇宙の構造形成問題』である。一番自然なシナリオは,「宇宙初期の密度揺らぎが自己重力で成長し,構造が形成される」とする説であるが,現在の大規模構造を完全に説明するまでに至っていない。この標準的理論の修正版を含めこれまで多くの試みがなされているが,我々は,まったく新しい観点からのアプローチが必要と考える。つまり,宇宙の構造形成問題を物理の基礎的な問題ととらえ,関連する物理的素過程を明らかにしなければその本質が解明されないのではないかと考える。より具体的に述べると,宇宙の構造形成問題を系統的,かつ総合的に研究するには,まずその物理的素過程に立ち戻り,各方面からいろいろな可能性を考え直す必要があると思われる。その際,現在最も必要とされる分野は,揺らぎの起源としての位相欠陥や量子場の揺らぎなどを明らかにする素粒子理論,宇宙の大規模構造を考える際に欠かせない宇宙論や一般相対論,およびその観測的データの提供,さらに自己重力多体系の緩和現象や構造形成問題の新しいアプローチとしてのカオス理論などが考えられるが,早稲田大学にはちょうどこの3分野に第一線で活躍する研究者がおり,特定課題の共同研究を行うにふさわしい状況にあった。そこで,本研究では,次の3つの基礎物理学的観点から構造形成の本質的問題を探り,宇宙の構造形成問題解明に迫った。(1)宇宙初期の相転移・インフレーションを含む素粒子的アプローチ。(2)宇宙の非線形構造形成問題を一般相対論を基礎に考察。(3)自己重力多体系の構造形成問題を非線形物理学,特にカオス理論の観点から考える。 94年度は,まず構造形成問題の基礎過程と考えられる3つの各アプローチに対し,グループに分かれ研究を進めた。素粒子論的観点から量子トンネル現象の基礎的理解およびその宇宙の相転移にともなう位相欠陥,ミニブラックホール形成問題との関連を大場が,また曲がった時空における量子場の振舞いを確率過程量子化の方法を用い金長が,さらにそれに基づきインフレーション宇宙論における密度揺らぎの起源の問題を前田,大場,金長が解析した。また,もう一つの素過程のカオス的アプローチとして,自己重力多体系における構造形成問題を相沢が,より一般的な構造形成問題とカオス理論の関係を宮坂が考察した。その宇宙論へ応用に関しては,前田が加わり検討を行った。第3の宇宙スケールの構造形成に不可欠と考えられる非線形構造形成の一般相対論的アプローチに関しては前田が,また宇宙背景輻射や銀河分布などの現在の構造に関する観測的情報は大師堂が担当した。これらの研究において,大規模なシミュレーション計算は不可欠で,購入したワークステーションおよびスーパーコンピューターを併用し,研究を進めた。また,95年度は,前年度の研究成果を持ち寄り,各アプローチの相互検討を行った。その後はお互いの連絡を密にし,総合的観点から各アプローチを共同で解析し,どの素過程が最も構造形成問題において本質的かつ重要であるかを調べ,宇宙の構造形成問題解明の可能性を探った。

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Overseas Activities

  • 宇宙のダークエネルギーと重力理論

    2012.04
    -
    2013.03

    フランス   APC 研究所

    イギリス   ケンブリッジ大学

    ニュージーランド   オークランド大学、カンタベリー大学

  • 重力物理学と宇宙論の最重要課題に関する研究

    2006.03
    -
    2006.09

    スペイン   バルセロナ大学

    イギリス   ケンブリッジ大学、ポーツマス大学